UC-NRLF 35 715 GIFT OF PROF. W.B. RISING SPECTRUM ANALYSIS. ELEMENTS OF MODERN CHEMISTRY. BY ADOLPHE WURTZ, MEMBER OF THE INSTITUTE, HONORARY DEAN AND PROFESSOR OF CHEMISTRY OF THE FACULTY OF MEDICINE OF PARIS, MEMBER OF THE ACADEMY OF MEDICINE, ETC. TRANSLATED AND EDITED, WITH THE APPROBATION OF THE AUTHOR, FROM THE FOURTH FRENCH EDITION, BY WM. H. GREENE, M.D., DEMONSTRATOR OF CHEMISTRY IN THE MEDICAL DEPARTMENT OK THE UNIVERSITY OF PENNSYLVANIA, MEMBER OF THE AMERICAN PHILOSOPHICAL SOCIETY, OF THE CHEMICAL SOCIETIES OF PARIS AND BERLIN, ETC. WITH ONE HUNDRED -\ND THIKTY-TW,0 JLLJJS^T RATIONS LONDON AND PHILADELPHIA: J. B. LIPPINCOTT & CO. 1880. (ALL RIGHTS RESERVED.) Copyright, 1879, by J. B. LIPPINCOTT & Co. AUTHOR'S PREFACE, THIS book is translated from the fourth French edition by my pupil and friend, M. Greene, whose perfect familiarity with the French language and thorough competence, at the same time, in chemistry I have had occasion to appreciate. The translation is, then, a faithful, or even improved, representation of the original work, in which he will certainly have detected and corrected some faults. The French editions succeed each other rapidly, showing that this little book responds to an educational need. It has been the endeavor to keep it up with the current of the latest discoveries, and in it to condense a considerable number of exact and well-selected facts, without banishing the theory which binds them together. Thus, the origin and foun- dation of the atomic theory have been given, as far as possible, in historical order. The notions concerning atomicity, so im- portant for the appreciation of the structure of combinations and for the interpretation of chemical reactions, are presented in an elementary form. The reader will remark that the history of the metalloids is relatively more developed than the remainder of the book. Indeed, this is the fundamental part of chemistry, and a fa- miliar knowledge of it is indispensable to the fruitful study of the metals and of organic chemistry. It is also the most at- tractive portion for beginners, for it is the most easily under- stood. Immediately on entering the immense domain of organic iii 237376 1V AUTHOR'S PREFACE. chemistry, we find the facts overwhelmingly numerous and complicated. Among all these facts a severe and careful choice has been made, the historical importance and the theo- retical and practical interest of the compounds described being borne in mind. In this respect many additions have been made to the third French edition. Thus, the question of isomerism, upon which the theory of atomicity has thrown so much light, has been treated in a more thorough manner. The chapter on the aromatic compounds has been considerably augmented. The author hopes that these " Elementary Lessons" will be well received by the new public to whom they are presented, and that they will contribute to render attractive and diffuse the knowledge of the science to which he has devoted his life. ADOLPHE WURTZ. PARIS, November 20, 1878. TRANSLATOR'S PREFACE. IT is a privilege to be able to bring before the English-read- ing public a work by one who has justly won the reputation of being the most able thinker and perspicuous teacher of France. M. Wurtz is the acknowledged leader of modern chemical philosophy, and his labors have firmly established many of the views which long remained unaccepted by the majority of chemists, but which are now regarded as essential to the science. This book is therefore a brief but accurate embodiment of modern chemical ideas, arranged in such a form that the most difficult principles are acquired gradually in the course of the descriptions. While the original has been carefully followed, a few slight changes and additions have been made. Some mineral sources not given in the French edition have been introduced, and a few processes to which greater attention is generally paid in English works have been more fully developed. WM. H. GREENE. TABLE OF CONTENTS. PAGE INTRODUCTION DISTINCTION BETWEEN CHEMICAL AND PHYSICAL AC- TION 7-9 DEFINITION OP CHEMISTRY 10 AFFINITY MOLECULES ATOMS 11-13 DECOMPOSITION DOUBLE DECOMPOSITION 17-20 LAW OF DEFINITE PROPORTIONS EQUIVALENTS MULTIPLE PROPOR- TIONS . 21-26 HYPOTHESIS OF ATOMS .26 GAY-LUSSAC'S LAW ATOMIC THEORY 27 AMPERE'S LAW AVOGADRO'S LAW 30-32 LAW OF SPECIFIC HEATS 34 LAW OF ISOMORPHISM . . .37 NOMENCLATURE AND NOTATION 37 Hydrogen 48 Oxygen 54 Ozone . . . 59 Air 63 Water 70 Mineral Waters 82 Sulphur and Compounds ........ 88-111 Selenium and Tellurium Ill Chlorine and Compounds 112-127 Bromine and Compounds ........ 127-130 Iodine and Compounds ........ 130-136 ANALOGIES OF CHLORINE GROUP 136 Fluorine Hydrofluoric Acid 136 Nitrogen Ammonia Oxides and Acids of Nitrogen . . 138-161 Phosphorus ........... 161 Arsenic 176 Antimony ............ 185 ANALOGIES OF NITROGEN GROUP 190 Boron 191 Silicon 194 Carbon 200 vii Viii TABLE OP CONTENTS. PAGE Compounds of Carbon and Hydrogen Structure of Flame . . 217 THEORY OF ATOMICITY 222 General Properties of Metals 231 Alloys 236 Oxides and Metallic Hydrates 238-245 Sulphides 245 Chlorides ..... . . 246 Salts '. . - .250 Richter's Laws . . . . . . ..""... . 253 BERTHOLLET'S LAWS 265 Nitrates Sulphates Carbonates 271-277 CLASSIFICATION AND ATOMICITY OP METALS 277 Potassium 282 Sodium 291 Lithium 299 Caesium and Rubidium SPECTRUM ANALYSIS 300 Thallium Barium . . 302 Strontium -'.,- . . 304 Calcium . . . *... . ; .: . 305 Magnesium . * . * . . . . .' . 310 Aluminium . . - V .' -. :". c . . . . 313 Clay and Pottery . .. .. V r-* - V-" - , . .317 Iron . . . . * . i' . . -, " ..-. . 318 Zinc . . . .,.'.. v . . V . . . 330 Gallium . . .-.'.'-* . . . - . . . 335 Indium . 336 Cadmium . . 337 Cobalt 338 Nickel 340 Manganese -.- . . . . . 342 Chromium . . -i . ->* >. .C . - . . 346 Bismuth 349 Tin 352 Lead .357 Copper ...... 368 Mercury 375 Silver 384 Gold 391 Platinum . . . v , . . v. . . . .395 ORGANIC CHEMISTRY TETRATOMICITY OF CARBON ..' . . ~ . . 399 HOMOLOGOUS BODIES .=..-*- . . . . . . 405 ELEMENTARY ANALYSIS 406 DETERMINATION OF MOLECULAR WEIGHT . . . . , . 410 ISOMERISM METAMERISM POLYMERISM 412 FUNCTIONS OF ORGANIC COMPOUNDS . . . . . . 414 Monatomic Compounds .- . . 415 Polyatomic Compounds . . . . ... . 426 Cyanogen Compounds ., . 429 TABLE OF CONTENTS. IX PAGE Compounds of Carbon Monoxide 438 Monatomic Alcohols and their Derivatives ..... 444 Saturated Hydrocarbons 470 Compound Ammonias 479 Organo-Metallic Compounds ........ 486 Volatile Fatty Acids and their Derivatives ..... 488 Polyatomic Compounds and their Derivatives 513 Series C n H 2n 517 Glycols 521 Glycerin 529 Polyatomic Acids 536 Uric Acid Series .......... 559 Higher Alcohols .......... 564 Sugars and Starches 567 Fermentation 577 Glucosides . . . . . .. . . . . . 586 Aromatic Compounds ......... 590 Derivatives of Benzol 602-638 Naphthalene 639 Anthracene ........... 640 Natural Alkaloids 643 Albuminoid Matters . 657 ELEMENTS OF MODERN CHEMISTRY. INTRODUCTION. THE material objects surrounding us present striking and infinite differences. Sulphur is readily distinguished from charcoal, rock-crystal from flint, iron from copper, water from spirit of wine, and wood from ivory. It is known to all that these bodies differ not only in form, density, and structure, but also in their proper substance. They differ, too, in the changes through which they pass under the same conditions. When subjected to the action of heat they receive very differently the impression of that force. They become heated more or less quickly, and transmit the heat with greater or less rapidity throughout their own substance. A short bar of iron cannot be grasped in the hand by one extremity if the other be heated to redness ; under the same conditions a cylinder of charcoal may be handled with impunity. Communicate sufficient heat to water and it is converted into steam ; remove heat from it, and if the cooling be sufficient, it is frozen into ice. Spirit of wine cannot be congealed by the most intense cold known. If a magnet be placed among iron filings they attach themselves in tufts around the two poles ; on the contrary, copper filings are indifferent to the magnetic attraction. Rock-crystal is transparent to light ; flint is opaque. These two bodies are unalterable by fire. They may be heated to red- ness in a furnace, but after the temperature has abated they will be found with their original characters unchanged. It is very different with the coal which we burn in our grates. This body disappears during the combustion, and leaves only a quan- tity of ashes. But it has not been destroyed, and its substance is found in entirety in a certain gas produced by the combus- tion. Like charcoal, sulphur is combustible, and is converted by burning into a gas, the suffocating odor of which is well known. Neither sulphur nor charcoal undergo any alteration when 8 ELEMENTS OF MODERN CHEMISTRY. exposed to damp air ; it is not the same with iron. In a moist atmosphere this metal experiences a striking and lasting change. Its surface becomes covered with rust and is no longer iron. In the forests, the leaves which fall and remain upon the moist soil are slowly consumed and disappear in the course of seasons. All of these changes, these phenomena, take place daily be- fore our eyes, and are familiar to all of us. On comparison, striking differences are discovered between them : some are but passing, and do not affect the proper nature of the body. They are the results of forces which act at sensible distances, and which leave the body in its primitive state as soon as their action has ceased. A piece of soft iron is attracted by the magnet before contact is established, and when under the mag- netic influence, is capable of attracting other soft iron in its turn : the action of the magnet has made the iron itself mag- netic, but it immediately loses this property when the magnet is withdrawn ; and further, this momentary change in property has brought about no alteration in the intimate nature of the iron. It is found after the experiment in precisely the same condition as before. In the same manner, rock-crystal undergoes no change in its specific identity by the passage of a ray of light. Withdraw from the vapor of water the heat which has been communi- cated to it, and the liquid water is recovered with all its prop- erties. Restore to the ice the heat which was abstracted in its formation, and water is regenerated as before. This is charac- teristic of the changes produced by physical forces. Under the influence of such forces, bodies experience modifications more or less profound, more or less lasting, but which never affect their specific nature. But the iron which rusts undergoes a complete and lasting change in its properties and in its substance. The rust is no longer iron, and vainly would it be sought to isolate the metal by mechanical means, or to discover its presence by the aid of the most powerful microscopes. The metal has disappeared as such ; it has undergone a complete transformation ; it has be- come another body. It has attracted one of the elements of the air, oxygen, and has, moreover, fixed to itself the moisture of the atmosphere. These latter bodies, which differ from iron in substance, have intimately united with the metal itself, and the result of this union, of this combination as it is called, is INTRODUCTION. 9 a new body, rust or hydrated oxide of iron. In this case the alteration is profound, the change is lasting ; the specific nature of the body is affected. This is characteristic of chemical action. In the same manner, when the charcoal and the sulphur are burned in the air ? they attract oxygen and combine with it, forming two new bodies that are called carbonic and sul- phurous acids. These phenomena may be rendered more clear by simple and well-known experiments. Experiment 1. A globe (Fig. 1) is filled with oxygen, a gas which constitutes one of the elements of the atmosphere, and which is eminently fitted to support combustion ; into it is plunged a morsel of charcoal lighted at one end ; immediately the coal glows with a brilliant light, the combination takes place actively, and the charcoal is rapidly consumed. But presently the light becomes paler, the combustion ceases, and the char- coal is extinguished. The oxygen is now nearly or quite con- FIG. 1. FIG. 2. sumed, and the globe is filled with another gas which is no longer oxygen, although it contains that oxygen. It contains also the matter of the charcoal which has disappeared, and these two bodies have combined to form a new body, which is carbonic acid. This latter will not support combustion, and further, it extinguishes burning bodies. It is then a body having entirely new properties, and is formed by a chemical action. Experiment 2. Into another jar filled with oxygen (Fig. 2) is plunged a spoon containing ignited sulphur. The combus- A* 10 ELEMENTS OP MODERN CHEMISTRY. tion takes place with a beautiful blue flame, and in burning in the oxygen with so much energy, the sulphur unites with the gas and forms with it a new body, which is called anhydrous sulphurous acid. It is a suffocating gas, which extinguishes flame. It reddens, and afterwards bleaches, a solution of blue litmus poured into the jar. These are special properties which do not belong to the oxygen at first contained in the jar. They characterize a new body, the result of the combination of the sulphur with the oxygen, and formed by chemical action. Carbon, sulphur, and oxygen are simple bodies or elements. They are so called because from neither of them can more than one kind of matter be obtained. But when the charcoal in burning unites with the oxygen, the carbonic acid which re- sults from the union contains two kinds of matter, carbon and oxygen ; and these two elements are united in such an intimate manner that the body which contains both does not resemble either carbon or oxygen: it is endowed with new properties which do not in any manner recall those of the elements which constitute it. In fact, it is a new substance, a compound body formed by the combination of the matter of the charcoal with the matter of the oxygen. Considering the preceding facts, we may give to chemistry the following definition : chemistry studies those intimate ac- tions of bodies upon each other which modify their natures and cause a complete and lasting change in their properties. Iron may be reduced to a fine powder. This may be mixed with sulphur itself reduced to powder, and if the mixture be sufficiently intimate, it will present neither the lemon-yellow color of sulphur nor the gray-black of finely-divided iron. Nevertheless, a homogeneous substance cannot be formed in this manner. If the powder be examined under the micro- scope, the particles of iron may be recognized disseminated among those of the sulphur, but not confounded with them. By the aid of a magnet the iron may be separated. On the other hand, if the mass be thrown into water, the particles of iron will sink first to the bottom, while the lighter particles of sulphur remain in suspension. Thus, after having triturated the sulphur and iron together, not only can each substance be recognized in the mass, but they can be again separated by mechanical means. Here there has been no chemical action, but simply a mixture. If, however, this mixture be heated, the sulphur will first be seen to melt, and afterwards the INTRODUCTION. 11 whole mass will blacken and enter into fusion if the tempera- ture be sufficiently elevated. After cooling, it is perfectly ho- mogeneous, and neither iron nor sulphur can be recognized. Both have disappeared as such, and in their place is found a substance having new properties ; it is the sulphide of iron. They have disappeared, but their substance is not lost ; and it may be proved by experiment that the weight of the sul- phide of iron produced is exactly equal to the sum of the weights of the iron and the sulphur. The ponderable matter of the iron is then added to the ponderable matter of the sul- phur, and has formed with it a union so intimate that there results a new body, the smallest particles of which are per- fectly similar to each other and to the entire mass. This ex- ample and a thousand others that might be given prove that when bodies combine there is neither loss nor creation of mat- ter. The result of the combination, that is, the compound body, contains the whole of the substance and nothing more than the substance of the combining bodies. This is an essen- tial characteristic of chemical combination. The force which presides over chemical combination is called affinity. It is important that this force be distinguished from another which is often opposed to it, and which is cohesion. In order to reduce to powder a solid substance, such as pyrites or sulphide of iron, it is necessary to overcome the resistance opposed by the particles of the mass to their separa- tion. This resistance is due to a special force, which brings and maintains in relation to each other the homogeneous par- ticles of the sulphide of iron, as indeed of all solid bodies. This is cohesion. The particles which are bound together by this force are not only those minute particles which are visible to the naked eye or under the microscope, and of which the most impalpable powder of a solid body is composed. Such particles still present a magnitude that can be measured ; they must be considered as little masses, so to speak, indivisible by the mechanical means at our command, but formed in reality of particles still smaller. These smallest particles of a solid body which are bound by cohesion are called molecules. They are not in immediate contact with each other. In a perfectly compact and homogeneous mass, such as sulphide of iron, the molecules do not touch each other. Between them exist spaces of considerable magnitude, compared to the real volume of the molecule. This idea must not be confounded with po- 12 ELEMENTS OF MODERN CHEMISTRY. rosity, which is caused by those accidental spaces which form visible pores in solid bodies. These intermolecular spaces are those which separate the molecules of a homogeneous and com- pact solid body, and physicists have further been led to believe that even in solid bodies the molecules are not perfectly immo- bile, but that they execute vibratory movements in the spaces which separate them, at the same time maintaining their own relative positions. If a solid body be heated, a part of the heat is employed in raising the temperature, another part serves to increase the distances which separate the molecules : the body expands in becoming heated. But, as the distances between the molecules increase by the action of the heat and the effect of the expan- sion, the molecular attraction necessarily becomes more feeble. Cohesion is thus somewhat diminished, and if the heat be further increased, it may be so much diminished that the mole- cules, which have thus far been maintained in definite rela- tions, can move and glide freely over each other; the solid body then enters into fusion : it becomes a liquid. The liquid state is produced by a diminution of cohesion, and is charac- terized by a greater mobility of the molecules. But if the liquid body be still further heated, at a certain point the additional heat may produce such a separation of the molecules that, already freed from all mutual attraction, they become completely independent of each other. This is char- acteristic of the gaseous state. It may be stated, then, that cohesion is considerable in solid bodies, but slightly energetic in liquids, and null in gases, and we have just seen that heat, by causing the changes of state of a body, can overcome and even practically abolish this physical force. Chemical force or affinity is at the same time more intimate and more powerful. It modifies the molecules themselves. It brings heterogeneous substances into intimate relations, and thus produces new molecules. A consideration of the examples already cited may indicate more clearly the meaning of this important proposition. We have brought together sulphur and iron, and by their reciprocal action and the aid of heat there has been formed a new body, sulphide of iron. We know that the smallest mass of sulphur we can obtain is composed of a collection of per- fectly homogeneous molecules, aggregated by cohesion. In each INTRODUCTION. 13 of them but one kind of matter can be found. It is the same with iron : the particles of this metal are perfectly homoge- neous. Sulphur and iron are simple bodies or elements. Let us now consider the sulphide of iron which results from their combination. This body also is formed of a collection of molecules, bound together by cohesion and perfectly similar to each other, but not homogeneous, for in each molecule we dis- tinguish two kinds of matter, sulphur and iron. It cannot be admitted that these two substances are con- founded in the molecule, or that the effect of the combination of sulphur with iron is an interpenetration of the two bodies so intimate that they both disappear in what might be called a homogeneous mixture. On the contrary, it is supposed that the combination results from the juxtaposition of two infinitely small masses, each of which possesses a real magnitude and a constant weight. These little masses that no force, chemical or physical, can divide further, constitute the atoms. In each molecule of sul- phide of iron there exist two of these masses, one of sulphur and one of iron ; and the atom of sulphur and the atom of iron are bound together, but not confounded, by chemical force. And when sulphur combines with iron it is because the atoms of the sulphur arrange themselves in juxtaposition with those of the iron, and it is affinity which brings about the action. When these atoms again separate, the sulphide of iron is said to decompose. When it attracts the atoms of another body, it is said to combine with that body. If sulphide of iron remain for some time exposed to moist air, its surface becomes covered with an efflorescence formed of a saline matter. In this case it has attracted one of the ele- ments of the air, oxygen, with which it has combined to form green vitriol or sulphate of iron. The molecules of oxygen, upon which cohesion has no hold, the body being gaseous, are each formed of two atoms, but these atoms are of the same kind ; the molecules of sulphide of iron, on the contrary, are each formed of two unlike atoms, one of sulphur and one of iron. These latter attract four atoms of oxygen, which constitute two molecules of that gas, and these group themselves around the atom of sulphur and the atom of iron, forming with them one single molecule, more complex than the primitive molecule of sulphide of iron, for it contains in addition four atoms of oxygen. 2 14 ELEMENTS OF MODERN CHEMISTRY. 1 molecule 1 molecule 1 molecule sulphide of iron. oxygen. oxygen. fixes and there results 1 molecule ilpliate of iron. ^ It is seen from what precedes that the words molecule and atom are far from being synonyms. The chemical molecule constitutes a whole of which the atoms form the parts, and these atoms are held together by affinity. In the preceding figure, this exchange of affinities between the atoms is indi- cated by lines of union. Chemical molecules have been well compared to edifices: the atoms constitute the materials, and it is readily conceived that such molecular edifices differ from each other according to the nature, number, and arrangement of the atoms, that is, the materials composing them. An edifice may be enlarged by the addition of new parts : it may be reduced in size or it may be entirely demolished. In the same manner a chemical molecule may be increased by the annexation of new atoms, or diminished by the separation of some of those which it already contains. In the first case there is combination, in the second, decomposition. We may still further consider these phenomena of combina- tion and decomposition. Since the combination of two bodies results from the recip- rocal action of their atoms, and has for effect a change in the nature of the molecules, it is evident that it can only take place when these atoms, and consequently the molecules, are brought into intimate relations ; or more precisely, when the molecules of one of the bodies enter within the sphere of action of the molecules of the other body. And this sphere of action is very limited, for the affinity or elective attraction of the atoms is only exercised at infinitely small distances. INTRODUCTION. 15 It results that affinity is often retarded by cohesion, which maintains the relations between the molecules of a solid body. These two forces are frequently in opposition, and that the first may attain the supremacy it is necessary that the other shall yield. To make manifest or to increase the affinity be- tween two bodies, it is then necessary to diminish their cohe- sion. On this condition the molecules can enter within the spheres of their reciprocal attraction, and the atoms of one body can attract those of the other. It has been seen from one of the experiments already cited that in order to combine iron with sulphur it is necessary to elevate the temperature. Now, the heat, by fusing the sul- phur, diminishes its cohesion, and, giving its molecules freedom of motion, puts them into more intimate contact with those of the iron. Chemical action then commences. Instead of heating the sulphur and iron to bring about chemical action, it would be sufficient to moisten the mixture with water. By the intervention of this liquid the particles of sulphur and of iron are, as it were, cemented together and thus brought into more intimate relations. For a stronger reason can chemical action between two solids be facilitated by dissolving them both in water and mixing the solutions. Dis- solved, they themselves assume the liquid state and lose, in great part, their cohesion. The ancients understood the in- fluence of the liquid state upon reactions, and stated it with exaggeration : Corpora non.agunt nisi soluta. Although the liquid state facilitates chemical reactions, it does not follow that it always determines them. Frequently liquids and even gases, after being mixed, must be heated before they will react upon each other. Experiment. In a glass tube (Fig. 3) two gases, oxygen and hydrogen, are mixed in the proportion of one volume of the first to two of the second. Although the mixture is per- fectly homogeneous and very intimate, and although the cohe- sion of the gaseous molecules is null, no action takes place. But as soon as the mixture is heated by approaching a lighted taper to the mouth of the tube, combination takes place ener- getically. An explosion occurs and the two gases unite, form- ing water. In this case the heat has determined combination by increasing the intensity of the movements which animate the molecules of each gas, and so bringing the molecules of the one within the sphere of attraction of those of the other. 16 ELEMENTS OF MODERN CHEMISTRY. The electric spark produces the same effect, and it probably acts by the heat which it communicates to the mixture. FIG. 3. More rarely combination is brought about by the influence of light. If a small bottle be filled with a mixture of equal volumes of hydrogen and chlorine gases, and then thrown into the air so that it may be struck by the direct rays of the sun, the combination of the two gases takes place instantly and with explosion. Such are some of the conditions which favor or determine chemical combination. Let us now study the circumstances which accompany these phenomena. Experiment. If sulphur be strongly heated in a small glass flask until it begins to boil, and some copper turnings be then thrown into the flask, a brilliant incandescence takes place im- mediately. It is produced by the combination of the two bodies. Charcoal, sulphur, and phosphorus produce a brilliant light when they are burned in oxygen. Their combination with the gas takes place with evolution of luminous heat. Whenever a combustible body of whatever nature burns in the air, the heat and light are developed by the combination of the body with oxygen, one of the elements of the air. In general, all chemical combinations give rise to the production of heat, more or less intense ; in certain cases it is luminous, but more often it is obscure ; sometimes it is scarcely perceptible. While heat acts as the determining cause of a great number INTRODUCTION. 17 of combinations, and while it is the result of such combination, it may play still another role in chemical reactions. In place of favoring combination, it may act in the opposite manner, separating atoms which are united by chemical attraction. Mercury retains indefinitely its brilliant surface when ex- posed to the air at ordinary temperatures, but at a temperature near its boiling-point it slowly attracts the oxygen of the air, and becomes covered with an orange-red powder, which is oxide of mercury. In this case heat has assisted the formation of a compound. If, however, this red powder be heated in a small retort to a temperature near redness, it is again resolved into mercury, which appears in drops in the neck of the retort, and into oxygen which may be collected. In this case an intense heat breaks up the compound which is formed at a temperature less elevated ; it occasions a decom- position. Heat acts thus in a great number of cases. A body is said to decompose when the elements composing it are separated from each other. The electric spark may occasion such separation when it is passed through compound gases. If a series of electric dis- charges be passed through ammonia gas, the latter is decom- posed, that is, resolved into its two elements, nitrogen and hydrogen. In like manner, the current of the voltaic pile decomposes a great number of chemical compounds, the elements of which separate and appear, each at its appropriate pole of the bat- tery. The decomposing action exerted by the galvanic current upon chemical compounds was discovered about the commence- ment of the present century by Nicholson and Carlisle. These physicists were the first to decompose water by the voltaic current. Lastly, light may decompose certain bodies, among which are a great number of the compounds of silver. The art of photography is founded upon the decomposing action of light upon certain of these combinations. There is a certain class of decompositions which it is impor- tant to consider with attention. They are occasioned by the intervention of more powerful affinities than those which main- tain united the elements of a compound body. If copper be heated in the air, it attracts oxygen and is con- 2* 18 ELEMENTS OF MODERN CHEMISTRY. verted into a black powder, a compound of oxygen and copper, which is called oxide of copper. The affinity which unites the two bodies is considerable ; it cannot be overcome by the ac- tion of heat alone ; at any ordinary temperature to which the oxide so formed may be exposed, the atoms of copper still re- main intimately associated with those of the oxygen. But if this oxide be mixed with powdered charcoal and then heated, a moment arrives when the affinity of the charcoal for the oxy- gen is superior to that of the copper. The atoms of oxygen then abandon the copper and combine with the charcoal, thus forming a new compound, carbonic acid, which is disengaged in the form of gas. Here there is at the same time decompo- sition and combination. The molecules of oxide of copper are decomposed ; those of carbonic acid are formed. Nothing is created in combinations ; nothing is lost in de- compositions. In the preceding experiment only copper re- mains ; the charcoal and oxygen have disappeared, but their substance is not lost. All of the matter of the charcoal is FIG. 4. found combined with all of the matter of the oxygen in the product of their combination, the carbonic acid, in such a manner that the weight of the latter added to the weight of the copper remaining, exactly represents the weight of the oxide of copper and charcoal. INTRODUCTION. 19 Experiment. Some oxide of mercury, of which we have seen the decomposition by heat, may be placed in a tube through which is passed a current of hydrochloric acid gas, a gas composed of chlorine and hydrogen (Fig. 4). An ener- getic reaction takes place. The orange-red powder is converted into a white crystalline substance, and much heat is produced. At the same time a small quantity of liquid condenses in the bulb. This is water, and the white powder formed is mercuric chloride, or corrosive sublimate, a compound of mercury and chlorine. The hydrochloric acid has converted the mercuric oxide into mercuric chloride. The mercury, at first combined with oxygen, is now combined with chlorine. But what has become of the oxygen ? It has combined with the hydrogen of the hydrochloric acid, forming water. We have brought into presence of each other two compound bodies : Mercuric oxide, Hydrochloric acid, and from their reciprocal action two new compounds result : Mercuric chloride, Water or oxide of hydrogen. This reaction has then occasioned an interchange of elements. The mercury of the mercuric oxide has combined with the chlorine of the hydrochloric acid, and the oxygen has left the mercury and combined with the hydrogen, which was aban- doned by the chlorine. The reaction has been as easy as energetic, thanks to the intervention of two affinities, for the affinity of chlorine for mercury has been aided by that of hy- drogen for oxygen. Two molecules are decomposed, and two new molecules are formed by an exchange which may be rep- resented in the following manner : BEFORE THE REACTION. Mercury + Oxygen = Mercuric oxide. Hydrogen + Chlorine = Hydrochloric acid. DURING THE REACTION. AFTER THE REACTION. Mercury + Chlorine = Mercuric chloride. Hydrogen + Oxygen = Water. 20 ELEMENTS OP MODERN CHEMISTRY. Such reactions, characterized by an interchange of elements, are called double decompositions. They are the more usual reactions in chemistry. The examples cited have been demonstrated by experiments easy to comprehend and to repeat, and are sufficient to give an idea of chemical phenomena. We have seen how, on the con- tact of two heterogeneous bodies, this elective attraction, which is called affinity and which sets in motion the smallest particles of bodies, comes into play to produce either combination or decomposition ; we have seen how this force modifies the chemical molecules either by interposing other molecules, or under the influence of physical forces, such as heat and elec- tricity. The study of all these phenomena constitutes chem- istry, the science of molecular changes ; a science grand in purpose and in magnitude, since it penetrates to the very nature of the bodies surrounding us ; a science unlimited in its applications, since through it we learn to know and control the powerful forces which are at work in the most intimate structure of matter. If we trace the acquired facts to the most obvious and most certain conclusion, we must admit the diversity of matter. There exists, indeed, a certain number of bodies, each of which, when submitted to the various tests resulting from the applica- tion of physical and chemical forces, furnishes but one and the same substance, and it is impossible to obtain anything else than this substance from the body. We maintain, then, until proved to the contrary, that each of these bodies contains but a single kind of matter, and they are called simple bodies or elements. The chemical forces reside, as has been seen, in the most remote particles, in the atoms of these bodies. In uniting together, the elements form compound bodies, and it has al- ready been stated that such combinations result from the juxta- position of the atoms which attract each other. The idea of atoms is an hypothesis, but the hypothesis is based upon nu- merous and important facts, which it weaves together in the most natural manner. It is more than an hypothesis : it is a theory. Chemists have universally adopted it, for it has ren- dered immense service to the science. Let us proceed, then, to a consideration of the facts upon which it is based. DEFINITE PROPORTIONS, EQUIVALENTS. 21 FIG. 5. DEFINITE PROPORTIONS, EQUIVALENTS. The proportions by weight according to which bodies combine are invaria- ble for each combination Those proportions are the equivalents Ex- periments demonstrating this fact. Experiment. A test-glass (Fig. 5) contains a liquid which is universally known as sulphuric acid. Although largely di- luted with water, that is, mixed with a large quan- tity of that liquid, it still manifests its presence by energetic properties. It has a very sour and cor- rosive taste, a quality of an acid. If a few drops of blue litmus solution be added to it the blue color instantly changes to bright red. Another glass contains a solution of caustic potash or potassium hydrate. This substance possesses a strong, lye-like, alkaline taste, very easy to distinguish from that of the acid. The color of the blue litmus is not affected by this liquid, but if a few drops of the litmus solution, previously reddened by an acid, be added, the blue color is immediately restored. This caustic substance has properties which are different from those of acids, and which are called basic or alkaline properties. Potassium hydrate is an alkali or powerful base. If now the alkaline liquid, which has a blue color, be poured drop by drop into the acid, which is red, and the mixture be stirred with a glass rod, a moment arrives when the red color of the acid liquid changes to blue. Exactly at this moment we have a solution which has no action upon litmus ; it will not redden the blue solution, neither will it restore the blue color to the red. This may be demonstrated by dipping into it first a red and then a blue litmus-paper. Furthermore, this liquid possesses neither the acid taste of the oil of vitriol nor the alkaline taste of the caustic potash, but its taste is salty. By their mixture and reciprocal action the sulphuric acid and the potash have lost the energetic properties which they 22 ELEMENTS OF MODERN CHEMISTRY. manifested in the free state. They are exactly saturated ; they are neutralized. That is, the liquid which now contains both, or more properly the product of their reaction, is neither acid nor alkaline ; it is neutral, and its neutrality is manifested both by its indifference to vegetable colors and by its effects on our organs of sense. There is no excess, neither of sulphuric acid nor of potash, but the two bodies have reacted exactly upon each other and have both disappeared, and from their recipro- cal action two new bodies result, a salt called potassium sul- phate, and water. Whenever sulphuric acid is thus saturated by potash, there arrives a moment when the whole of the acid is precisely neu- tralized by the alkali, and when the two bodies are converted, without residue of either one or the other, into potassium sul- phate and water ; and it is always easy to recognize the instant at which this effect is produced by the action of the liquid upon vegetable colors, such as solution of litmus, or syrup of violets. The latter is reddened by an acid, changed to green by an alkali, and assumes its natural violet tint when the neutral point is reached. Now, it has been found that this last effect is only produced when the acid and the alkali are mixed in certain proportions, which remain invariable, whatever may be the quantities which are mixed. In other words, it has been found that the quantities of sulphuric acid and potash which reciprocally neutralize each other and form potassium sulphate, maintain a constant ratio to each other. It may be easily proved that when the state of neutrality has been once attained, it is immediately passed and disturbed by the least excess of either acid or base that may be added to the liquid. This is made evident by the immediate change in the color of the liquid to either red or green. Thus, in order to form sulphate of potassium with a given quantity of sulphuric acid, it is necessary to add an invariable quantity of potash ; and if the quantity of sulphuric acid be increased by a third, or in any proportion whatever, it is neces- sary to increase by a third, or in the same proportion, the quan- tity of potash. Experiments of this kind have been made with other acids and other bases, and have introduced into the science the fun- damental notion that these bodies react upon each other in definite proportions to form salts, and that consequently the composition of the latter bodies is perfectly fixed. A given DEFINITE PROPORTIONS, EQUIVALENTS. 23 quantity of any acid whatever, invariably saturates a fixed quantity of the same base. This, then, is the first point. It may be added that similar researches made towards the close of the last century have led to a not less important result, namely, the respective" quantities of several acids which satu- rate a'given weight of one base are exactly proportional to the quantities of the same acids which saturate a given weight of another base. The law which governs the composition of salts was discovered towards the close of the last century by a Ger- man chemist, Richter. We cannot now expose it in detail ; such development will be better placed and better understood in that part of this work which treats of the formation of salts. For the present it is sufficient to state that die law mentioned is a consequence of the law of definite proportions, and that the latter law is universal. It applies not only to the reaction of acids upon bases, but is true for all chemical combinations. It may be thus expressed : The relative weights according to which bodies combine are invariable for each combination. There is one feature of the laws which control the composi- tion by weight of bodies that it is important to comprehend well. It may be best illustrated by experiment : 100 gr. of mercury are put into the presence of chlorine gas, a body possessing very powerful affinities. In this man- ner mercuric chloride or corrosive sublimate is formed, and it is found that 35.5 gr. of chlorine are necessary to convert 100 gr. of mercury into this compound. These figures 100 and ."..'." express the invariable ratio in which these elements are combined in corrosive sublimate. Here we have the definite proportions. Now let the 135.5 gr. of corrosive sublimate be dissolved in water, and a plate of copper be placed in the solution ; this metal will displace the mercury, and combining with the 35.5 gr. of chlorine will form with it cupric chloride, which will remain in solution, coloring the liquid green. The 100 gr. of mercury are then precipitated, and it will be found that 31.75 gr. of copper have entered the solution and actually combined with 35.5 gr. of chlorine. Into this solution of cupric chloride a plate of zinc is now plunged ; all of the copper is precipitated in its turn, and 33 gr. of zinc enter into combination with die 35.5 gr. of chlorine, forming zinc chloride. 24 ELEMENTS OF MODERN CHEMISTRY. The 35.5 gr. of chlorine have now been combined success- ively with 100 gr. of mercury, 31.75 gr. of copper, 33 gr. of zinc. These numbers, which express the respective quantities of mercury, copper, and zinc which combine with the same quan- tity of chlorine, may be called the equivalents of these metals. In fact, these quantities are equivalent to each other in relation to the same quantity of chlorine, the experiment having shown us that in order to displace 100 gr. of mercury combined with 35.5 gr. of chlorine it is necessary to employ 31.75 gr. of copper or 33 gr. of zinc. To continue, 100 gr. of mercury are combined with oxygen, and it is found that this quantity of the metal requires 8 gr. of oxygen to form the red powder called mercuric oxide. But how much oxygen is necessary to form cupric oxide with 31.75 gr. of copper? Remarkable as it seems, exactly 8 gr. are required, and 8 gr. are also requisite to form oxide of zinc with 33 gr. of zinc. 100 gr. of mercury, 31.75 gr. of copper, 33 gr. of zinc, which are equivalent compared to 35.5 gr. of chlorine, are then also equivalent in relation to 8 gr. of oxygen. Chlorine itself may be oxidized, and there exists a gaseous compound of chlorine and oxygen which contains precisely 8 gr. of oxygen for 35.5 gr. of chlorine. Thus, there are required 35.5 gr of chlorine to form chlorides with. 8 gr. of and also 8 gr. of oxygen to oxidize ....... zinc, . ( iJ^ ( 33 gr. of zi 8 gr. of oxygen to oxidize 35.5 gr. of chlorine. In general, if A, B, C, combine with D, A, B, C, combine also with E, and further, D combines with E, the letters A, B, C, D, E, representing the weights of the dif- ferent elements which enter into combination, or the propor- tions according to which the bodies combine among themselves. MULTIPLE PROPORTIONS. 25 They are expressed by numbers that have been called combin- ing weights or equivalents ; these represent the ratio of weights or the relative weights. They are indeed relative to a unit which has served as a term of comparison, and which is the equivalent of hydrogen. That is, the quantity of hydrogen which combines with 35.5 of chlorine being 1, the equivalent quantities of oxygen, zinc, copper, and mercury will be repre- sented by the numbers 8 33 31.75100. These are the facts of experiment. Let 33 gr. of zinc be treated with hydrochloric acid, the latter is immediately de- composed ; its chlorine combines with the zinc, forming chlo- ride of zinc, and its hydrogen is disengaged. In this experi- ment the hydrogen of the hydrochloric acid is simply displaced by the zinc. Now, 33 gr. of this metal will displace exactly 1 gr. of hydrogen. It is seen that the numbers which have been given do not express absolute quantities, but merely the relative weights ac- cording to which the bodies combine or replace each other in compounds, these relative weights being compared to that of hydrogen, which is taken as unity. Such is the signification of the numbers. inn QI *. OQ oz t (which represent 100 31.75 33 3o.5 j the equivalents. of of of of of of mercury, copper, zinc, chlorine, oxygen, hydrogen. This being admitted, in order to determine the equivalent of an element it is sufficient to find the quantity of that ele- ment which combines either with 1 of hydrogen or with a quantity of another element which is equivalent to 1 of hydro- gen, for instance, 8 of oxygen. The notion of equivalents can be understood from the pre- ceding considerations ; it appears as a consequence of the law of definite proportions ; it comprehends certain facts relative to the laws of the composition of bodies, but it by no means represents the full scope of these laws. The following devel- opments add important features. MULTIPLE PROPORTIONS. Two bodies may combine in several proportions. Thus, with oxygen, carbon forms two compounds, both of which are gaseous. The less rich in oxygen is carbon monoxide ; the richer is carbon dioxide, or carbonic acid gas. Dalton was thf B 3 26 ELEMENTS OF MODERN CHEMISTRY. first to perceive that for the same quantity of carton, carbonic acid contains exactly twice as much oxygen as carbon monoxide. He made analogous observations concerning the composition of two compounds of carbon and hydrogen, the monocarbide of hydrogen or marsh gas, and the dicarbide of hydrogen or olefiant gas. "From these observations he deduced the law of multiple proportions, which may be thus stated : when two bodies, simple or compound, unite in several proportions to form several compounds, the weight of one of these bodies being considered as constant, the weights of the other vary according to a simple ratio. Thus, taking up one of the examples given above, carbon unites with oxygen in two proportions : Carbon monoxide contains 16 parts of oxygen to 12 parts of carbon. Carbon dioxide contains 32 parts of oxygen to 12 parts of carbon. The numbers 16 and 32 are in the ratio of 1 : 2. Nitrogen forms five compounds with oxygen ; if such quan- tities of these compounds be taken as contain the same weight of nitrogen, the weights of the oxygen will be proportional to the numbers 1, 2, 3, 4, 5. Nitrogen monoxide contains for 28 parts of nitrogen 16 parts of oxygen. Nitrogen dioxide " 28 " " 32 " Nitrogen trioxide " 28 " 48 " " Nitrogen tctroxide " 28 " " 64 " " Nitrogen pentoxide " 28 " " 80 " These numbers, 16, 32, 48, 64, 80, are multiples of the first by the numbers 1, 2, 3, 4, 5. Five compounds of manganese and oxygen are known, and similar relations exist between the quantities of oxygen con- tained in these compounds. The first contains 55 parts of manganese to 16 of oxygen. The second " 55 " " 24 The third " 55 " " 32 " The fourth 55 " " 48 " The fifth " 55 " 56 The numbers 16, 24, 32, 48, 56 are in the simple propor- tion 1 : 1.5 : 2 : 3 : 3.5. Such is the law of multiple proportions discovered by Dalton. HYPOTHESIS OF ATOMS. The brilliant researches of Dalton did not terminate with the acquisition ot facts, but sought to account for them by a GAY-LUSSAC'S LAWS. ATOMIC THEORY. 27 theoretical conception. Taking up the old idea of Lysippus and the word of Epicurus, he supposed all ponderable matter to be composed of indivisible particles which he called atoms. He gave a precise meaning to the vague and ancient notion by considering on one hand that the atoms of each kind of matter, of each element, possess an invariable weight, and on the other that combination between different kinds of matter results from the juxtaposition of their atoms. Such is the atomic hypothe- sis, the substance of which we have already indicated in treat- ing of chemical phenomena in a general manner. It permits a simple and rational interpretation of the laws of the compo- sition of bodies, and establishes between these laws a firm bond of theory. Indeed, if the combination of bodies results from the juxta- position of their atoms, the latter being considered as indivisi- ble and possessing a constant weight for each element, it is evident that combination can only take place in definite pro- portions, for these proportions represent the invariable relations between the weights of the atoms which are in juxtaposition. If, on the other hand, one body may combine with another in several proportions, such combination can only take place by the juxtaposition of 1, 2, 3, 4, etc., atoms of one body with one or more atoms of the other. It evidently results that the weight of the latter body being constant, the weights of the other in these various combinations must be multiples of each other. An hypothesis which gives such a simple and precise ex- planation of the facts relative to definite and multiple propor- tions is surely worthy of attention. It acquires still further import and becomes elevated to the rank of a theory when to these facts are added others entirely different from the first, but not less important. GAY-LUSSAC'S LAWS. ATOMIC THEORY. Gases combine in simple volumetric proportions Relations which exist between the volumes of gases and their atomic and molecular weights Equal volumes of gases or vapors contain the same number of molecules The molecular weights are equal to double the densities compared to hydrogen. Among these new facts it is convenient to first notice those which were discovered by Gay-Lussac, from 1805 to 1808. They relate to the volumes of gases which combine together. 28 ELEMENTS OF MODERN CHEMISTRY. Experiment. 10 cubic centimetres of hydrogen and 5 cubic centimetres of oxygen are introduced into a tube (Fig. 6), which is inverted over the mer- cury-trough. The gaseous mixture occupies the up- per portion of the tube, which is an eudiometer. Into the upper extremity of this tube is hermeti- cally cemented a small iron wire with a little ball at each extremity. Another iron wire passes through the wall of the tube at a short distance from the upper extremity, in such a manner that the interior extremity of this second wire is opposite, and at a short distance from the lower ball of the superior and vertical wire. A little iron chain is at- tached to the exterior end of the horizontal wire, and dips into the mercury of the trough. Things being thus arranged, the inferior extremity of the eudiometer is closed by an iron cap, and the charged plate of an electrophorus is approached to the upper button. A spark instantly passes be- tween the two buttons in the eudiometer, and a bright flash is seen to fill the whole space occupied by the gaseous mixture. The combination of the two gases has taken place with the development of luminous heat. Water has been formed, and is condensed in drops too small to be perceptible. If now the eudiometer be opened, by removing the cap which closes it under the mercury, the latter at once rises to the top of the tube, and fills the whole of the space at first occupied by the hydrogen and oxygen. These gases have then combined exactly in the proportion of 10 volumes of the first to 5 of the second, or more simply, in the proportion of 2 volumes to 1 volume. If the eudiometer-tube be now surrounded by a wider glass tube, and the latter be filled with oil heated to 120, the heat GAY-LUSSAC'S LAWS. ATOMIC THEORY. 29 communicated to the eudiometer will be sufficient to convert into steam the water which was condensed, and it may be proved, all corrections being made, that the vapor occupies a volume equal to exactly 10 cubic centimetres ; that is, a volume equal to that of the hydrogen employed. From the facts thus established we draw the conclusion that 2 volumes of hydrogen exactly combine with 1 volume of oxygen to form 2 volumes of vapor of water. There is thus determined a simple ratio not only between the volumes of hydrogen and oxygen which combine, but further, between the volume of vapor of water formed and the sum of the volumes of the composing gases. 3 volumes of the latter are reduced to exactly 2 by the combination. Analogous facts have been discovered for other gases, as shown by the following examples : 2 volumes of nitrogen + 1 volume of oxygen = 2 volumes of nitrogen monoxide. 2 volumes of chlorine + 1 volume of oxygen = 2 volumes of chlorine monoxide. In other cases the combination of two gases determines a still greater contraction, and the initial volume is reduced one- half. Thus 1 volume of nitrogen + 3 volumes of hydrogen = 2 volumes of ammonia gas. Finally, when two gases combine in equal volumes, their combination usually takes place without contraction ; in other words, the volume of the gas produced is equal to the sum of the volumes of the component gases. From these collected facts we may draw the following general conclusions : 1. There is a simple relation between the volumes of gases which combine. 2. There is a simple relation between the sum of the volumes of the combining gases and the volume of the gas resulting from the combination. These laws were first signalized by Gay-Lussac, whose name is attached to them. Their importance is immense ; they have added a notable development to the atomic theory. If the definite proportions by weight in which bodies com- bine represent, according to Dalton, the relative weights of their atoms, it is natural to conclude that the definite and simple proportions by volume in which gases combine, accord- 3* 30 ELEMENTS OF MODERN CHEMISTRY. ing to Gay-Lussac, represent the volumes occupied by the atoms. Under the same volume gases would then contain the same number of atoms. This was first proposed by Am- pere, who based his conclusion on the important consideration that gases dilate and contract nearly equally when submitted to the same variations of temperature and pressure. Within certain limits the proposition is true ; it applies to a large num- ber of simple gases. But if equal volumes of these gases, measured, let it be well understood, under the same conditions of temperature and pressure, contain the same number of atoms, it is evident that the weights of these equal volumes should represent the weights of the atoms. In other words, the atomic weights of the simple gases should be proportional to their densities. The densities of gases and vapors represent the weights of these gases or vapors compared to the weight of an equal volume of air. To determine the density, a certain volume of the given gas is weighed, and this weight is divided by that of an equal volume of air, under the same conditions of tempera- ture and pressure. The air is then the unit to which are com- pared the densities of gaseous bodies. On comparing these densities to that of hydrogen, 1 which we take as unity, we find that the same numbers express almost exactly the densities and the atomic weights, the unit to which the densities are com- pared, that is, hydrogen, being the same as that to which are compared the atomic weights. The figures in the following table demonstrate this to be the case : ELEMENTS. Densities of Gases or Vapors, Air being Unity. Densities, Hydrogen being Unity. Atomic Weights. Hydrogen . . . . 0693 1 1 Oxygen 1.1056 15.9 16 Nitrogen Sulphur (density at 1000) Chlorine 0.9714 2.22 2.44 14 32 35.2 14 32 35.5 5 393 778 80 Iodine 8.716 125.8 127 1 To do this it is sufficient to multiply the densities of the gases compared to air by - - = 14.44, which is the density of the air compared to hy- drogen as unity. GAY-LUSSAC'S LAWS. ATOMIC THEORY. 31 It is seen from this table that if the densities of gases be compared to hydrogen as unity, just as the weights of their atoms are compared to hydrogen as unity, the same figures, or very nearly the same figures, express both the densities and the atomic weights. We may add that, for all the elements taken in the gaseous state, there has been determined between the densities referred to hydrogen and the atomic weights, if not equality, at least a simple ratio. These remarkable rela- tions were pointed out by (Jay-Lussac. Equal volumes of the simple gases above enumerated con- tain the same number of atoms. Two volumes of hydrogen, then, contain twice as many atoms as one volume of oxygen ; and when these gases combine in the ratio of 2 volumes of the first to 1 of the second, we must admit that each atom of oxy- gen combines with 2 atoms of hydrogen. We say, then, that water is composed of 2 atoms of hydrogen and 1 atom of oxy- gen. These three atoms so united constitute the smallest quantity of water that can exist in the free state. This is called a molecule of water. But what volume does this molecule occupy ? The experi- ment has shown us. We have seen that 2 volumes of hydro- gen, in combining with 1 volume of oxygen, yield 2 volumes of vapor of water. One molecule of water in the gaseous state, then, occupies 2 volumes, if 1 atom of hydrogen occupy 1 volume, and if 1 atom of oxygen occupy 1 volume. It is seen that the volumes represent the atoms, and the relative weights of equal volumes, that is, the densities, represent the weights of the atoms. Let us now consider another compound gas, ammonia, composed of hydrogen and nitrogen. A very simple experi- ment will show in what proportion the atoms of these elements are combined in this gas, and the volume occupied by the compound compared with the volumes of its compopent gases. Experiment. 100 volumes of ammonia gas are introduced into a tube inverted upon the mercury-trough (Fig. 7), and the walls of which are pierced at the upper end by two plati- num wires, between the ends of which a small space is left. To these wires are attached the extremities of the two con- ducting wires of a Ruhmkorff coil, and the current is passed so that a series of electric sparks traverses the ammonia between the extremities of the wires in the tube. The gas is imme- diately decomposed, and the level of the mercury in the tube 32 ELEMENTS OF MODERN CHEMISTRY. is depressed. When the experiment has terminated it is found that the volume of the gas has been doubled. Instead of 100 volumes, there are now 200, the gas being measured under the same conditions of temperature and pressure as before. It is found, by an analytical process that will be indicated further on, that these 200 volumes of gas resulting from the decompo- FIG. 7. sition of 100 volumes of ammonia are composed of 150 vol- umes of hydrogen and 50 volumes of nitrogen. These 150 volumes of hydrogen and 50 volumes of nitrogen are condensed by their union into 100 volumes of ammonia. In other words, 3 volumes of hydrogen and 1 volume of nitrogen are combined together in 2 volumes of ammonia. And as the volumes rep- resent atoms, it follows that in ammonia gas 3 atoms of hydro- gen are combined with 1 atom of nitrogen. But the quantity of ammonia containing 1 atom of nitrogen and 3 atoms of hydro- gen is the smallest quantity of ammonia that can exist. It is a molecule of ammonia, and this molecule occupies 2 volumes, if 1 atom of nitrogen or 1 atom of hydrogen occupy 1 volume. Here, then, is another compound gas, ammonia, of which the molecule occupies 2 volumes, like that of water. It is the same with all the gases. All of the atoms which are combined to constitute the molecule of a gas or vapor are so condensed that the molecule occupies the same volume as the molecule of vapor of water, or the molecule of ammonia. We may state, then, with the Italian chemist, Avogadro, that equal volumes of gases contain the same number of mole- cules, and that each of these molecules occupies 2 volumes, if 1 atom of hydrogen occupy 1 volume. It follows that the weight of 2 volumes of a compound gas represents the weight of its molecule, the weight of one volume of hydrogen GAY-LUSSAC'S LAWS. ATOMIC THEORY. 33 being 1. But the weight of 2 volumes of a gas or vapor is nothing more than the double of its density compared to hy- drogen ; for the density is the weight of 1 volume compared with the weight of 1 volume of hydrogen. To find the weight of the molecule (the weight of 2 volumes) of a gas or vapor, it is then only necessary to multiply its density compared to hydrogen (the weight of 1 volume) by 2. The densities of gases and vapors are generally referred to air as unity. To bring them to the hydrogen standard, they are multiplied by the number expressing the relation of the density of hydrogen to that of air, which is -o.-oVoT 14.44. The product thus obtained expresses the density compared to hydrogen, that is, the weight of 1 volume. To find the weight of 2 volumes, or the molecular weight, it is then only necessary to multiply the densities compared to air by twice the ratio of the density of the air compared to hydrogen, that is, by the constant factor, 0.0693 0.0693 28 88. It is seen that if the atomic weights of certain gases can be deduced from a comparison of their densities, this same physi- cal notion may also serve for the determination of the molecu- lar weights of compound gases. The numbers which represent double the densities of gases or vapors compared to hydrogen, express also the molecular weights of these gases or vapors, that is, the weight of all the atoms in the molecule, the weight of one atom of hydrogen being 1. Considering the examples already given, we may deduce the molecular weights of water and of ammonia from the densities of steam and ammonia gas. The density of vapor of water, determined by Gay -Lussac- is 0.6235. To find the molecular weight of water, it is suffi- cient to multiply this figure by 28.88. The product, 18, ex- presses the weight of a molecule of water, which is indeed composed of 2 atoms of hydrogen ....... =2 1 atom of oxygen ....... =16 1 molecule of water ....... =18 Sir Humphry Davy found for the density of ammonia the B* 34 ELEMENTS OF MODERN CHEMISTRY. number 0.5901. This being multiplied by 28.88, the product, 17.04, should represent the weight of one molecule of am- monia. Ammonia contains 3 atoms of hydrogen ....... 3 1 atom of nitrogen 14 1 molecule of ammonia 17 The discovery of the laws which govern the combination of gases by volume has seconded in the most efficacious manner the progress of the atomic theory. In the first place, it has established a marked distinction be- tween the old idea of equivalents and the modern one of atoms. The equivalents represented merely the ponderable proportions according to which bodies combine ; the atomic -weights repre- sent the relative weights of the volumes of gases which com- bine. The equivalent of hydrogen unity expressed merely that hydrogen was the unit to which were referred the weights of other bodies with which it entered into combination. The atomic weight of hydrogen is the weight of one volume of hydrogen, taken as unity, and to this unit are referred the atomic weights of other bodies. In the second place, the discovery of Gay-Lussac has shown how the atomic weights of simple bodies and the molecular weights of compound bodies can be determined from the den- sities of gases and vapors. However, this resource would be insufficient in very many cases. It only applies to gaseous bodies, or such as can be conveniently converted into vapor. Now, there are many sub- stances with which this is impossible, and serious difficulties would be encountered in the determination of the atomic weights of certain elements were it not for another physical law, discovered by two French physicists, Dulong and Petit. It denotes the relations which exist between the specific heats and the atomic weights. LAW OF SPECIFIC HEATS. It is known that in order to raise the temperatures of differ- ent bodies through the same number of thermometric degrees very different amounts of heat are required. Thus, one kilo- gramme of water requires 30 times more heat than one kilo- gramme of mercury to raise its temperature one degree, and if the quantity of heat required to raise the temperature of LAW OF SPECIFIC HEATS. 35 one kilogramme of water one degree be represented by 1, the quantity required to raise the same weight of mercury one degree will be represented by 0.0333 = -j^. This fraction ex- presses the specific heat of mercury between and 100. The specific heat of a solid or liquid body is then the amount of heat required to raise the temperature of a certain weight of the body one degree, the amount required to raise the tempera- ture of an equal weight of water one degree being taken as unity. In 1820, Dulong and Petit discovered the remarkable fact that if the figures which express the atomic weights of the elements, liquid or solid, be multiplied by those which express their specific heats, the product obtained is sensibly constant ; in other words, the specific heats of the elements are inversely as their atomic weights. It results that if such quantities of the elements be taken as represent their atomic weights, the amount of heat required to raise the temperature of each one degree will be sensibly the same. The law discovered by Du- long and Petit may then be expressed, the atoms of the solid elements possess sensibly tfte same specific lieats. This law permits the deduction of the atomic weights from the specific heats. Indeed, it is evident that if the product of the specific heats by the atomic weights be a constant, that may be called the atomic heat, dividing this product by the specific heat should give the atomic weight. The product which represents the atomic heat is 6.4, very nearly, as may be seen from the following table : Products of the NAMES OF THE SOLID ELEMENTS. Specific Heats. Atomic Weights. Specific Heats by the Atomic Weights. Atomic Heats. Sulphur, between and 100 . . 0.2026 32 6.483 Selenium 0762 79 5 6 058 Tellurium 0.0474 129 6 115 Bromine, between 78 and 20 0.0843 80 6.744 Iodine, between and 100 . . 0.0541 127 6.873 Phosphorus, between + 1 and 30 0.1887 31 5.850 0814 75 6 105 Carbon, diamond, at 600 . . . 0.46 12 5.52 Boron, crystallized, at 600 . . 0.5 11 5.5 Silicon at 1000 .... 20? 28 5 66 Potassium 1695 39.1 6 500 36 ELEMENTS OP MODERN CHEMISTRY. TABLE. Continued. NAMES OF THE SOLIJ> ELEMENTS. Specific Heats. Atomic Weights. Products of the Specific Heats l>y the Atomic Weights. Atomic Heats. Sodium, between 34 and + 7 . Lithium ... 0.2934 9408 23 7 6.748 6 586 Thallium 03355 204 6 844 Magnesium ... ... 2499 24 5 998 Aluminium 2143 27 5 786 1217 65 6 693 Iron 0110 56 6 116 09555 65 2 6 230 05669 112 6 349 Cobalt 1068 59 6.301 Nickel 1089 59 6 424 Tungsten 0334 184 6 146 0722 96 6.931 0314 207 6 499 0308 210 6.468 09515 63.5 6.042 05077 122 6.193 Tin 05623 118 6.635 Mercury, between 77.5 and 44 Silver 0.03247 0.05701 200 108 6.494 6.157 Gold 0324 197 6.383 Platinum 03293 197.5 6.503 0.0593 106.5 6.315 03063 199.2 6.101 Rhodium . 05803 104.4 6.058 0.03259 198 6.452 Carbon, silicon, and boron have long been regarded as ex- ceptions to Dulong and Petit's law. Their specific heats had been determined at comparatively low temperatures, and the products of the numbers obtained by the atomic weights fell much below 6.4. These exceptions have disappeared ; the ex- periments of M. Weber have shown that the specific heat of carbon, silicon, and boron increases with the temperature, and that for the first two elements it attains a limit, where it re- mains sensibly constant. The figures given in the preceding table for these three elements are those of M. Weber, and it is seen that on multiplying them by the respective atomic weights of carbon, silicon, and boron, values are obtained which are sensibly near 6.4. It will otherwise be remarked that there are sensible differ- ISOMORPHISM. CHEMICAL NOMENCLATURE, ETC. 37 ences between the numbers expressing the atomic heats of the various solid elements, showing that Dulong and Petit's law, although true in its generality and striking in its enunciation, is not free from certain perturbations which give to it the character of an approximate law. It is the same with other physical laws, Mariotte's law, for example. ISOMORPHISM. While considering the atomic theory and the determination of the relative weights of the ultimate particles of bodies, we cannot pass in silence a discovery which has had a great influ- ence upon the development of that theory. It is due to E. Mitscherlich, who, in 1819, made known the law of isomor- phism. This law may be thus stated : there is such a relation between the atomic constitutions of compound bodies belonging to the same group and their crystalline form, that " the same number of atoms combined in the same manner produce the same crystalline form, the latter being independent of the chemical nature of the atoms, and determined solely by their number and arrangement." The importance of the proposition as regards the atomic structure of bodies is self- evident. We will reconsider it when treating of the general characteristics of salts, but we may remark here that it has been of great value in the determination of certain atomic weights. Indeed, in some cases considerations of a chemical nature cannot decide between two numbers for the atomic weight of a given element. The choice is then determined by the following considerations : such a value must be attributed to the atomic weight that the isomorphous compounds formed by the element and by another to which it is analogous, may be represented by similar atomic formula. CHEMICAL NOMENCLATURE AND NOTATION. GENERAL CONSIDERATIONS. Sixty-four substances are now known which can be resolved into no simpler forms of matter, and which are consequently considered as simple bodies or ele- ments. By combining together, they form an innumerable mul- titude of compound bodies containing two or more elements. 4 38 ELEMENTS OF MODERN CHEMISTRY. In order to distinguish these bodies from each other it is neces- sary to give a name to each, for each constitutes a distinct sub- stance. The names of the simple bodies have been chosen at will, and in some cases recall some peculiar property of the sub- stances designated. It was formerly the same with compound bodies ; there was no definite rule for their nomenclature. From this there resulted a great complication of words which embarrassed the exposition of ideas, and often for the same sub- stance there were a number of synonyms, of which the least inconvenience was to uselessly fatigue the memory. Hence chemists have felt the necessity of a regular nomenclature, applicable to compound bodies, and capable of indicating their composition. Such is the principle of the chemical nomen- clature suggested by Guyton de Morveau, and developed by Lavoisier, Berthollet, and Fourcroy. This nomenclature, with some modifications, introduced by the progress of the science, is still adopted. Independently of this language, the rules of which will presently be detailed, chemists have adopted a written nota- tion which expresses in concise form the atomic constitution of compounds. The name of each element is represented by a symbol, which also expresses one atom t)f the substance. This symbol is the initial letter of the name of the element, or the initial letter with another when the names of two ele- ments begin with the same letter. Thus, H represents one atom of hydrogen weighing 1 ; represents one atom of oxygen weighing 16. By combining these symbols together, it is easy to represent in a precise manner the atomic compo- sition of compound bodies. From such combinations result chemical formulas, the use of which was introduced into the science by Berzelius. In the following table will be seen the names of the ele- ments now known, together with their atomic weights, and the symbols by which the atoms of the elements are represented in the notation. The greater number of the elements possess certain physi- cal properties which characterize them as metals. They are opaque, and possess a peculiar lustre, which does not disappear under the burnisher. They are good conductors of heat and electricity. CHEMICAL NOMENCLATURE AND NOTATION. 39 NAMES OF THE ELE- MENTS. 1 Atomic Weights. NAMES OF THE ELE- MENTS. Symbols. Atomic Weiglits. Aluminium . . . Al 27.5 Mercury (hydrar- Antimony (stibi- gyrum) . . . Hg 200 um) Sb 122 Molybdenum Mo 96 Arsenic .... As 75 Nickel .... Ni 59 Barium .... Ba 137 Niobium .... Nb 94 Bismuth .... Bi 210 Nitrogen .... N 14 Boron Bo 11 Osmium .... Os 199.2 Bromine .... Br 80 Oxygen .... 16 Cadmium . . Cd 112 Palladium . . Pd 106.6 Caesium .... Cs 133 Phosphorus . . . P 31 Calcium .... Ca 40 Platinum . . . Pt 197.5 Carbon .... C 12 Potassium (kalium) K 39.1 Cerium .... Ce 92 Rhodium .... Rh 104.4 Chlorine .... Cl 35.5 Rubidium . . . Rb 85.2 Chromium . Cr 52.5 Ruthenium . . . Ru 104.4 Cobalt .... Co 59 Selenium .... Se 79.5 Copper .... Cu 63.5 Silicon .... Si 28 Didytniuin . Di 96 Silver (argentum) Ag 108 Erbium .... Er 112.6 Sodium (natrium) Na 23 Fluorine .... Fl 19 Strontium . . . Sr 87.5 Gallium .... Ga 69.9 Sulphur .... S 32 Glucinium . . . Gl 9.5 Tantalium . . . Ta 182 Gold (auruin) . . Au 197 Tellurium . . . Te 128 Hydrogen . . . H 1 Thallium. . . . Tl 204 Indium .... In 113.4 Thorium .... Th 234 Iodine .... I 127 Tin (stannum) . . Sn 118 Iridium .... Ir 198 Titanium . . . Ti 50 Iron (ferrum) . . Fe 56 Tungsten (wolfra- Lnnthanium . . La 92 mium .... W 184 Lead (plumbum) . Pb 207 Uranium .... Ur 120 Lithium .... Li 7 Vanadium . . . V 51.37 Magnesium . . . Mg 24 Yttrium .... Y 89.6 Manganese . Mn 55 Zinc Zn 65.2 Zirconium . . . 1 Zr 90 Other elements, fewer in number, do not possess these prop- erties. They have been called the non-metallic bodies, some- times the metalloids. They include the following : HYDROGEN. OXYGEN. NITROGEN. SULPHUR. PHOSPHORUS. CHLORINE. SELENIUM. ARSENIC. BROMINE. TELLURIUM. ANTIMONY. IODINE. (BISMUTH ?) FLUORINE. SILICON. CARBON. From a theoretic stand-point this distinction presents but 40 ELEMENTS OF MODERN CHEMISTRY. little value, for it is impossible to draw an exact line sepa- rating the metals from the non-metallic bodies. NOMENCLATURE OF COMPOUND BODIES. The principle of chemical nomenclature is to indicate the composition of com- pound bodies by their names. Among such compounds the most numerous and the most important are those containing oxygen. They are binary or ternary ; that is, the oxygen in them is combined with one or two other elements. Binary Oxygen Compounds. We will first consider the more simple oxidized bodies, those which result from the com- bination of oxygen with but one other element, metallic or non-metallic. These compounds are called oxides, and differ as the element associated with the oxygen is metallic or non- metallic. In combining with non-metallic elements, oxygen generally forms compounds which are the anhydrides of acids, that is, compounds capable of uniting with water to form acids ; with the metals it forms metallic oxides. Experiments. 1. A small piece of phosphorus is placed in a capsule floating on the surface of mercury. It is ignited and the capsule covered with a bell-jar (Fig. 8). The phos- phorus burns, giving off a thick smoke, which condenses in FIG. 8. white flakes on the sides of the bell-jar. This substance re- sults from the combination of the phosphorus with the oxygen of the air : it is phosphorus pentoxide, or phosphoric anhydride. CHEMICAL NOMENCLATURE AND NOTATION. 41 2. If lead be heated in the air and maintained for some time in a state of fusion, its brilliant surface becomes tarnished and covered with grayish particles, which are finally converted into a yellow powder. This body is formed by the combina- tion of the lead with oxygen : it is plumbic oxide, or oxide of lead. But, as we have seen, such combination can take place in different proportions. An atom of a body may unite with 1, 2, 3, or more atoms of oxygen, and the names of the com- pounds so formed should indicate the degree of oxidation. Sulphur forms two compounds with oxygen : one contains 2 atoms of oxygen to 1 atom of sulphur ; the other, 3 atoms of oxygen to 1 of sulphur. They are designated by the names sulphurcws oxide, or anhydride, and sulphuric oxide, or anhy- dride. The written notation represents them by the symbols SO 2 , so 3 ; which express their atomic compositions. The number of atoms of any element is indicated by a small figure placed after and a little above or below the symbol of that element. The degree of oxidation is then expressed by the termina- tion in ous or ic of the name of the other element, which indicates the kind of oxide, ic denoting the superior oxide. Mercury forms two compounds with oxygen. The first contains 2 atoms of mercury for 1 of oxygen ; the second, 1 atom of mercury to 1 of oxygen. They are designated by the names and symbols as follows : Mercurous oxide Hg' 2 0. Mercuric oxide HgO. The names monoxide, sesquioxide, dioxide, etc., as will be seen further on, are also employed. 1 A monoxide is a combination of 1 atom of metal with 1 atom of oxygen. A sesquioxide " " 2 atoms " " 3 atoms " A dioxide " " 1 atom " " 2 " It is easy then to understand the signification of the follow- ing names and symbols : 1 The prefixes proto, biordeut, and ter have been, and are yet, frequently employed instead of mono, di, and tri. 4* 42 ELEMENTS OP MODERN CHEMISTRY. Manganese monoxide MnO. Manganese sesquioxide Mn 2 O s . Manganese dioxide MnO 2 . The oxide most rich in oxygen is sometimes called the per- oxide. Oxygen Acids and Metallic Hydrates. The oxygen com- pounds that we have just considered may unite with the ele- ments of water to form more complex compounds, which are ternary, that is, they contain three elements. To the two ele- ments of the oxide is then added a third, independently of the oxygen of the water, that is, its hydrogen. The oxygen acids usually result from the union of water with the non-metallic oxides. Experiment. Sulphur trioxide or sulphuric anhydride occurs in white silky tufts. It is very volatile, and if a bottle containing it be opened, its vapor comes in contact with the moist air and forms thick white fumes. If a small quantity of this substance be thrown into water, it immediately disappears and combines with that liquid. So great is the energy of the reaction that the heat disengaged gives rise to the production of steam, which, being suddenly formed and condensed in the midst of the cooler liquid mass, causes a peculiar noise, a sort of hissing. When the sulphuric oxide is dissolved in the water, the solution presents a very acid reaction. It contains sulphuric acid, the compound long known under the name of oil of vitriol. This reaction may be represented in the abbreviated lan- guage of the notation, which expresses the atomic composition of bodies with so much precision. The formula of sulphuric anhydride or sulphur trioxide is SO 3 ; that of water is H 2 0. Then if sulphuric acid result from the addition of all of the elements of water to those of sulphuric trioxide, it should contain SO 3 -f H 2 == H 2 S0 4 . This is a chemical equation, and it is seen that the two terms of the first member express the atomic composition of the reacting bodies, while the single term of the second mem- ber gives the atomic composition of the product of the reac- tion. Such an equation accounts for all of the atoms, and CHEMICAL NOMENCLATURE AND NOTATION. 43 the sum of all of the atoms written in the first member must exactly balance the sum of all those written in the second. There is a compound known as nitric anhydride, or nitrogen pentoxide. It results from the combination of nitrogen with oxygen, and its atomic composition is represented by the formula N 2 5 . In combinin with water it forms nitric acid. _|_ H 2 = 2(HN0 3 ). Nitric anhydride. Water. Nitric acid. (1 molecule.) (2 molecules.) These examples, which could be indefinitely multiplied, give an idea of the constitution of the ternary oxygen acids. The rules which have been already given for the nomenclature of the oxides apply also to the nomenclature of the acids. We have phosphorous acid and phosphoric acid. .H^po-phosphor- ous acid is an acid of phosphorus containing still less oxygen than phosphorous acid. (Hypo, literally, under.) The metallic hydrates result from the combination of water with the metallic oxides. It is well known that when quick- lime is sprinkled with water it becomes heated, increases in volume, cracks into pieces, and is finally converted into a white, impalpable powder, which constitutes slaked lime, a com- pound of the lime with water. Lime is the oxide of a metal called calcium. In combining with water it forms a ternary compound of calcium, hydrogen, and oxygen ; this is hydrate of calcium, or, as it is commonly called, hydrate of lime. CaO -f H 2 = CaH 2 2 . Calcium oxide. Water. Calcium hydrate. (Lime.) The metal potassium, the radical of potash, forms with oxy- gen a compound which contains two atoms of potassium com- bined with one atom of oxygen. The composition of this body is then represented by the formula K 2 O. It combines with water with great energy, and forms with it potassium hydrate or caustic potassa. K 2 O + H 2 == 2KOH. Potassium oxide. Water. Potassium hydrate. (2 molecules.) Oxygen Salts. The oxygen salts result from the action of the oxygen acids upon the oxides or upon the metallic hydrates. Experiment. The formation of a gait may be illustrated by a modification of one of the experiments already described. A quantity of dilute nitric acid is slightly reddened by a so- 44 ELEMENTS OF MODERN CHEMISTRY. lution of blue litmus or syrup of violets. 1 Some dilute solution of caustic potassa is also treated with the same coloring matter ; the syrup of violets will assume a green color, or blue litmus will remain unchanged. The latter liquid, which is alkaline, is now added drop by drop to the acid, until the red color disappears, giving place to the violet color of the syrup of violets or the blue of the litmus. The liquid is now neutral. It contains neither free nitric acid nor free potassa. Both have disappeared as such ; they are reciprocally neutralized, the first having lost its acid taste, the second its extreme caustic properties. They have produced a body having a saline, cooling taste, and exerting no action upon vegetable colors. It is a neutral salt which has been formed. It is called potassium nitrate. It is the nitre or saltpetre of the ancient chemists. It is not, however, the sole product of the reaction. Water is formed at the same time, and if we would comprehend the entire phenomenon, the reaction will be expressed by the following equation : HNO 3 -f KOH = KNO 3 + H 2 0. Nitric acid. Potassium hydrate. Potassium nitrate. Water. It is seen that the salt, potassium nitrate, is a ternary com- pound, similar in constitution to nitric acid itself. On com- paring the two formulae, HNO 3 nitric acid, KNO 3 potassium nitrate, it is seen that they only differ by the K in the second occupy- ing the place held by the H in the first. It may then be said that potassium nitrate represents in a manner nitric acid in which the hydrogen has been replaced by an equivalent quan- tity of potassium. This definition applies to the entire class of compounds under consideration. A salt represents an acid of which the hydrogen has been wholly or partially replaced by an equivalent quantity of metal. The acids constitute the salts of hydrogen : they are neu- tralized when this hydrogen is replaced by a metal. The acid or hydrogen salt differs from the metallic salt. From a theoretic point of view, an acid is a compound of the same order as a salt, and if these bodies are separated by such great differences 1 An infusion of common purple cabbage may be substituted for syrup of violets. CHEMICAL NOMENCLATURE AND NOTATION. 45 of properties, this is due to the nature of the base. What a difference, indeed, between hydrogen gas and the metals ! We have studied the formation of a salt by the action of an acid, nitric acid, upon a metallic hydrate, potassium hydrate. The anhydrous oxides may also form salts by reacting with the acids. Experiment. Yellow oxide of lead, when digested with dilute sulphuric acid, is converted into a white, insoluble pow- der, which is lead sulphate. This is a salt, but it is not the only product of the reaction, for water is formed at the same time. H 2 SO + PbO = PbSO 4 + H 2 0. Sulphuric acid. Lead oxide. Lead sulphate. Water. Lastly, among other modes of formation of salts, there is one which is worthy of interest, and of which an idea may be ob- tained from the following example. Sulphur trioxide, or sulphuric anhydride, combines energetic- ally with barium oxide or baryta, and from the union of all of the elements of both compounds there results a salt, barium sulphate. SO 3 4- BaO = BaO,S0 3 or BaSO 4 . Sulphur trioxide. Barium oxide. Barium sulphate. But, whether this salt be formed under these conditions, or by the action of sulphuric acid, its composition only differs from that of the latter acid by the substitution of Ba for H 2 . H 2 S0 4 sulphuric acid, hydrogen sulphate, BaSO* barium sulphate. The reactions which we have just studied, and which indicate the principal methods of the formation of salts, are sufficient to make clear the definition before given, that salts are derived from acids by the substitution of a metal for hydrogen. The nomen- clature defines and preserves these relations. To distinguish the different salts of the same acid, the name of the metal is placed first, and this is followed by the name of the acid, which is but slightly changed, ic is changed to ate, and ous to ite. Thus Sulphuric acid gives sulphates. Nitric acid " nitrates. Perchloric acid " perchlorates. Sulphurous acid " sulphites. Hyposulphurous acid " hyposulphites. These generic names follow the names of the metals which enter into the composition of the salts, and which specify them, as it were. Thus, we have : 46 ELEMENTS OP MODERN CHEMISTRY. Potassium sulphate, copper sulphate, lead sulphate, etc. ; Sodium sulphite ; Potassium nitrate, barium nitrate, silver nitrate, etc. But we know that a single metal may form several com- pounds with oxygen. In reacting upon the same acid these different oxides give rise to the formation of different salts. Thus, two different sulphates of copper are obtained, as sul- phuric acid is caused to react with cuprous oxide, or with cupric oxide. H-'SO* + Cu 2 = Cu 2 SO* -f IPO. Sulphuric acid. Cuprous oxide. Cuprous sulphate. Water. H-'SO + CuO = CuSO 4 + IPO. Cupric oxide. Cupric sulphate. It is easy to distinguish these two salts from each other by using the adjectives cuprous and cupr-ic before the substantive sulphate. Thus, we have mercuroits and mercuric sulphates ; ferrous and ferric sulphates. The preceding considerations will give an idea, sufficient for the time being, of the constitution and the nomenclature of salts. Their further exposition will be completed farther on. Nomenclature of Non-Oxygenized Compounds. The non- metallic elements other than oxygen can combine among them- selves or with the metals. Such compounds are designated by the name of one of the elements followed by the abbreviated name of the other terminating in ide. Thus, the compounds of the metals with chlorine, bromine, iodine, sulphur, arsenic, and carbon are called chlorides, brom/cfes, iodides, sulph/c^es, arsenides, carbides. We thus have sodium chloride, potassium bromide, lead iodide, zinc arsenide, iron carbide. The termi- nation uret was formerly used in place of ide. But a non-metallic body, such as chlorine or sulphur, can, like oxygen, form several compounds with the same metal. In these compounds 1 atom of metal may be united with 1 or 2 atoms of sulphur, or with 1, 3, or 5 atoms of chlorine, or again with 2 or 4 atoms of chlorine. Such atomic composition is expressed by the following names and symbols : Iron wjoHosulphide FeS. Iron bisulphide FeS 2 . Phosphorus fn'chloride PCI 3 . Phosphorus ^Htachloride PCI 5 . Tin tftchloride SnCl 2 . Tin teJrachloride ... SnCl*. Antimony fn'chloride SbCl 3 . Antimony joen/achloride SbCl 5 . CHEMICAL NOMENCLATURE AND NOTATION. 47 The names thus express precisely the number of atoms of the second element in combination with 1 atom of the first. The compounds of chlorine, bromine, iodine, and several other elements with hydrogen are acids ; they readily exchange their hydrogen for a metal, so forming compounds that are analogous to the oxygen salts, and which constitute the haloid salts of Berzelius. Experiment. The compound of chlorine with hydrogen is hydrochloric acid ; it is a gas, and dissolves in water, forming a fuming, strongly-acid liquid. When it is carefully poured into a concentrated solution of caustic potassa there appears a white precipitate, formed of little crystals and presenting the appearance of a salt. This is potassium chloride. It is formed according to the following reaction, and its formation is at- tended by the production of heat : HC1 + KOH = KC1 + H 2 0. Hydrochloric Potassium Potassium Water, acid. hydrate. chloride. The hydrogen compounds of bromine, iodine, fluorine, sul- phur, etc., possess analogous properties. They are called Hydrobroraic acid HBr. Hydriodic acid HI. Hydrofluoric acid HF1. Sulphydric acid or sulphuretted hydrogen . . . H 2 S. The chlorides may combine among themselves. It is the same with the bromides, iodides, sulphides, etc. If a solution of potassium chloride be poured into a concentrated solution of platinic chloride, a yellow precipitate, constituting a com- pound of the two chlorides, is formed. It is the double chlo- ride of platinum and potassium, or potassium platino-chloride. There exist, likewise, double sulphides formed by the union of two simple sulphides. Such compounds constitute what are called sulphur salts. Alloys and Amalgams. The compounds of the metals with each other are called alloys. Amalgams are the alloys of mercury, that is, the compounds of this liquid metal with another metal. 48 ELEMENTS OF MODERN CHEMISTRY. HYDROGEN. Density compared to air 0.0693. Atomic weight (1 volume taken as unity) H = 1. This body was discovered in 1*766 by Cavendish. It is one of the elements of water, hence its name, which was given by Lavoisier. Experiments. 1. A small piece of sodium is passed under a tube filled with mercury and inverted on the mercury-trough ; it rises to the top of the jar, and some water is then introduced (Fig. 9). As soon as the water touches the sodium a brisk disengagement of gas is ob- served ; this is hydrogen, produced by the decomposition of the water, and the reaction by which it is set at liberty is expressed in the following equation : 2H 2 + Na 2 = 2NaOH + H 2 . FlO. 9. Water. Sodium. Sodium Hydrogen. hydrate. If the tube be now inverted and a lighted taper be rapidly brought to the orifice, the gas will burn with a pale flame. A piece of reddened litmus-paper plunged into the water con- tained in the tube has its blue color at once restored, and this change is produced by the sodium hydrate or caustic soda dissolved in the water. 2. Some thin sheet-zinc cut into small pieces is introduced into a rather large test-jar (Fig. 10), and some hydrochloric acid is then poured upon it. A rapid eifervescence imme- diately takes place, and if a lighted taper be brought to the mouth of the jar, the stream of hydrogen evolved takes fire. This hydrogen is produced by the decomposition of the hydro- chloric acid by the zinc, which is converted into chloride. 2HC1 + Zn Hydrochloric Zinc. acid. (2 molecules.) ZnCP + H 2 . Zinc Hydrogen, chloride. HYDROGEN. 49 Preparation. A reaction analogous to the preceding is turned to advantage for the preparation of large quantities of hydrogen. Dilute sulphuric acid is de- composed by zinc. A two-necked bot- tle is about half filled with water, and gran- ulated zinc, or sheet- zinc cut into small pieces, is introduced; sulphuric acid is then added in small quan- tities by the aid of a funnel-tube which dips under the surface of the water (Fig. 11). The reaction at once commences, and hydrogen is disen- gaged. When the air at first contained in the bottle has been entirely expelled, the gas may be collected in jars or bottles filled with water and in- verted on the pneu- matic trough. In this reaction the zinc disappears and dissolves in the liquid with evolution of heat, and it often happens, if the liquid be sufficiently concentrated, that colorless crystals of zinc sulphate are formed on cooling. This salt and hydrogen are the sole products of the reaction of pure zinc upon sulphuric acid largely diluted with water. H 2 S0 4 + Zn = ZnSO* + H 2 . Sulphuric acid. Zinc. Zinc sulphate. Hydrogen. Physical Properties. Hydrogen is a colorless gas, and when pure has neither taste nor odor. It is the lightest of all known bodies, its density compared to air being 0.0693 ; that is, if one volume of air weigh 1, one volume of hydrogen, measured under the same conditions of temperature and pres- c 5 FIG. io. 50 ELEMENTS OF MODERN CHEMISTRY. sure, weighs only 0.0693. Hydrogen is then 14.44 time The weight of one litre of hydrogen at lighter than air. FiG. 11. and under the normal pressure is 0.0895 gramme. Instead of comparing the densities of gases and vapors to that of air, it is preferable to compare them to that of hydrogen taken as unity (page 30). Hydrogen passes with great facility through vegetable and animal membranes, and through porous substances that are im- pervious to water. It cannot be kept in a glass vessel that presents the least crack, for it would pass through much more readily than air. This property is expressed by saying that hy- drogen is very diffusible. According to Magnus, it is the only gas gifted with an appreciable conductibility for heat ; in this respect it is related to the metals. From a consideration of its physical properties and its combined chemical properties, Fara- day long ago announced the metallic character of hydrogen. This theoretic prediction has recently received a remarkable confirmation. Hydrogen, which was long regarded as incoerci- ble, has been liquefied and even solidified. Cailletet, of Paris, obtained it in the form of a cloud by exposing it to a pressure of 300 atmospheres at a temperature of 29 and then sud- denly relieving the pressure. Raoul Pictet, of Geneva, has advanced still further. By an apparatus of incomparable power, he subjected it to a temperature of 140 under a pressure of 650 atmospheres. Under these circumstances, hy- drogen was liquefied, and was visible as a steel-blue, liquid jet HYDROGEN. 51 at the moment of its projection from the tube in which it was condensed. The cold produced by its passage from the liquid to the gaseous state was so great that a portion of the liquid was solidified, and fell to the ground in metallic grains, producing a shrill sound as it struck the floor. Another portion of the solidified hydrogen remained in the tube during several minutes. Among the physical properties of hydrogen may be men- tioned the remarkable faculty it possesses of passing through plates of iron or platinum at high temperatures (H. Sainte- Claire Deville and Troost). It is well known that it rapidly passes through thin sheets of caoutchouc. According to Graham, this property is related to that possessed by certain solid bodies, and particularly metals, such as iron, platinum, and palladium, of absorbing hydrogen gas. This chemist designated the phenomenon by the name, occlusion of hydro- gen by the metals. Palladium especially is distinguished by the energy with which it absorbs hydrogen. It can condense in its pores nine hundred times its own volume of the gas. A palladium wire may be charged with hydrogen by arranging it in a voltameter so that it constitutes the negative pole of a small battery, the positive pole being a stout platinum wire. When the current passes, the hydrogen set at liberty at the negative pole (see page 71) is condensed in the palladium. This metal undergoes at the same time a remarkable change. Its volume augments and its density diminishes, but its metallic lustre remains, as do also, to a certain degree, its tenacity and con- ductibility for electricity ; besides this it becomes magnetic. There is thus formed a sort of alloy of palladium and hydro- gen, containing about 20 volumes of palladium to 1 volume of hydrogen reduced to the solid state. The density of this solid hydrogen compared to that of water, according to the determi- nations of Troost and Hautefeuille, is 0.62 : it is a little greater than that of lithium. Graham insisted upon the metallic char- acter of hydrogen thus alloyed with palladium, and proposed for it the name hydrogenium. Chemical Properties. Hydrogen is a combustible gas, and the product of its combustion is water. Experiments. 1 . A lighted taper may be thrust into a rather wide tube filled with hydrogen (Fig. 14). The gas takes fire on contact with the flame, but the taper is extinguished in the atmosphere of hydrogen. It may be relighted by withdrawing it through the burning gas. The experiment shows at the 52 ELEMENTS OF MODERN CHEMISTRY. same time that hydrogen is inflammable and that it is incapa- ble of supporting combustion itself. 2. A gas-bottle, A (Fig. 12), is arranged for the preparation of hydrogen, and water, zinc, and sulphuric acid are intro- FIG. 12. duced. The hydrogen evolved is made to traverse the tube CB, which is filled with fragments of chloride of calcium ; after having been dried by this substance, which is very avid of water, the gas escapes by the tube a, the end of which is drawn out to a point. The jet of gas is lighted, and burns with a pale flame. A bell-jar, D, is now held over the burning jet, and the sides of the glass soon be- come covered with dew, the drops of which unite and run down to the edge of the j ar. This is water, and it is formed by the combustion of the hydrogen ; that is, by its combination with the oxygen of the air. 3. A jet of hydrogen may be lighted by holding in it a tuft of asbestos which has been dipped in platinum black, that is, finely-divided platinum. The con- densation of the hydrogen in the pores of the finely-divided metal is so rapid that the platinum becomes heated to redness, and then ignites the gas. FIG. 13. HYDROGEN. 53 4. A tube filled with hydrogen may be held in the vertical position, bottom upwards, without the gas escaping rapidly by the inferior opening. If the tube be inclined, the hydrogen overflows and escapes upwards through the air. It may then be received in a second tube held vertically above the first, which is inclined more and more (Fig. 13). The passage of the gas into the upper tube can be demonstrated by approach- ing to the latter a lighted taper, when the hydrogen will burn with a faint explosion. Before igniting or collecting hydrogen escaping from a gen- erator, it should always be ascertained that the whole of the air has been expelled, otherwise dangerous explosions may result. 5. The explosions may take place with the production of a harmonious sound, if they are made to succeed each other Fia. 14. Fia. 15. rapidly and at regular intervals. These conditions are realized by burning a small jet of hydrogen in a somewhat large tube (Fig. 15). The flame is drawn away from the jet by the draft in the tube, but immediately recedes as the ascending hydro- 54 ELEMENTS OF MODERN CHEMISTRY. gen gas mixes with the air, at the same time producing a faint explosion, and the rapid succession of these explosions produces a musical tone. The hydrogen condensed in palladium appears to have some chemical properties different from those of gaseous hydrogen (Graham). It combines in the dark and at ordinary tempera- tures with iodine and chlorine ; the direct union of ordinary hydrogen with iodine is impossible, and with chlorine it takes place at the common temperature only under the influence of light. It seems, then, that hydrogen, when associated with palladium, is more active than in the ordinary state. OXYGEN. Density compared to air 1.1056. Density compared to hydrogen 16. Atomic weight =16. Oxygen was discovered, in 1 I 7'74, by Priestley, who obtained it by heating red precipitate or mercuric oxide. Experim ent. A tube, a (Fig. 16), contains a concentrated so- 'lution of the dis- infecting powder known as chlo- ride of lime ; a small quantity of the peroxide of cobalt, a com- pound of oxygen with the metal cobalt, is then introduced, and the whole is gen- tly heated. A brisk efferves- Fm 1G cence takes place, and if a match which has been just blown out and still presents a spark of fire OXYGEN. 55 be thrust into the mouth of the tube, it is instantly relighted, and burns with great brilliancy. This effect is due to a gas which is being disengaged, and which, to use the expression of Lavoisier, is eminently fitted to support combustion. It is the gas to which that great chemist gave the name oxygen. It is produced by a very simple reaction. Under the influence of the peroxide of cobalt, the calcium hypochlorite which is contained in the chloride of lime is converted into calcium chloride and oxygen. CaCPO 2 = CaCP + O 2 . Calcium hypochlorite. Calcium chloride. Oxygen. Preparation. Large quantities of oxygen may be prepared by a process analogous to the preceding. When potassium chlorate is heated, it is converted into potassium chloride, and gives up all of its oxygen. To facilitate this decomposition, a small quantity of manganese dioxide is mixed with the chlo- rate. The part taken by the manganese dioxide is analogous to that of the cobalt peroxide in the preceding reaction, and is not thoroughly understood ; it is most probable that it serves to distribute the heat more regularly through the mass of chlorate. If the temperature be sufficiently elevated, the de- composition of the chlorate is complete, and takes place accord- ing to the following equation ; KCK) 3 KC1 + O 3 . Potassium chlorate. Potassium chloride. Oxygen. The operation may be conducted in a glass retort, which should be about one-third filled with the mixture of chlorate and dioxide ; to the beak of the retort is adapted a delivery- tube, which dips under the surface of the water or mercury in the trough (Fig. 17). The retort is then heated by an alco- hol or gas lamp, and the chlorate melts and disengages its oxy- gen with effervescence. Towards the close of the operation, the heat is increased in order to decompose into potassium chloride and oxygen any potassium perchlorate that may have been formed by the union of a portion of the evolved oxygen with some of the chlorate. To make larger quantities of oxygen for filling the gas- holders of laboratories, etc., a mixture of potassium chlorate and manganese dioxide is heated in a sheet-iron or copper retort. At a bright red heat manganese dioxide gives up a third 56 ELEMENTS OP MODERN CHEMISTRY. of its oxygen, and is converted into the red oxide of manga- nese. 3Mn0 2 Mn 3 4 + O 2 . Manganese dioxide. Red oxide of manganese. Oxygen. Oxygen can be cheaply manufactured on the large scale by the process of Tessie du Mottay. This depends upon the for- mation of sodium manganate by the action of air upon a heated FIG. 17. mixture of manganese dioxide and caustic soda, and the subse- quent decomposition of this manganate at about 450 by a current of steam, a decomposition which again sets at liberty the oxygen absorbed by the manganese dioxide to form sodium manganate. The operation is continuous. Physical Properties. Oxygen is a colorless, odorless, taste- less gas ; it is a little heavier than the air. If one volume of hydrogen weighs 1, the same volume of oxygen, measured under the same conditions of temperature and pressure, weighs 16. This is expressed by saying that the density of oxygen compared to that of hydrogen is 16. A litre of oxygen weighs 1.437 gr. at and under the normal pressure. Until lately oxygen had been considered as a permanent gas. By subjecting it to a pressure of 300 atmospheres and a tem- perature of 29, and then suddenly relieving the pressure, Cailletet obtained it in the form of a cloud. Raoul Pictet liquefied it by a pressure of 300 atmospheres and a temperature OXYGEN. 57 of 140. He attributes to liquid oxygen a density near that of water, about 0.9787. Oxygen is but slightly soluble in water. A litre of water dissolves 0.041 litre, or 41 cubic centimetres, at ; 0.032 litre at 10 ; 0.028 litre at 20. The fractions 0.041, 0.032, 0.028, represent the coefficients of solubility of oxygen in water at the temperatures of 0, 10, and 20. Chemical Properties. Oxygen combines directly with most of the other elements, and the union often takes place with such energy that there results a great evolution of luminous heat : it gives rise to the phenomenon of combustion. Experiments. A cone of charcoal of which the point is red- hot is plunged into a globe filled with oxygen (Fig. 18), and immediately combustion takes place with great brilliancy. The oxygen combines with the carbon, forming a colorless gas, which is carbonic acid gas. In like manner, sulphur and phosphorus burn in oxygen, the first producing a colorless, irritating gas known as sulphurous FIG. 18. FIG. 19. acid gas, the second emitting thick fumes, which condense in white flakes of phosphoric oxide. A watch-spring may be drawn out into a spiral, and a small piece of tinder attached to one end ; after igniting the tinder, the spiral is rapidly plunged into a bell-jar filled 'with oxygen, and resting upon a plate containing a layer of water (Fig. 19). The tinder burns energetically, and heats the end of the spiral to redness ; then the combustion of the iron itself commences, and goes on with unparalleled brilliancy, and a production of c* 58 ELEMENTS OP MODERN CHEMISTRY. heat so intense that the oxide of iron formed melts and falls in incandescent drops, which fuse themselves into the sur- face of the plate, even after having traversed the layer of water. In the same manner, the combustion of the metal magnesium may be effected in oxygen ; it takes place with dazzling splen- dor, and gives rise to the production of a white powder, which is magnesia, or magnesium oxide. The preceding experiments are examples of rapid combus- tion. We have seen that solid substances, such as charcoal, iron, and magnesium, become incandescent in combining with oxygen : it is the phenomenon of fire. We have also seen that vapors, like those of sulphur and phosphorus, become lumi- nous in their combination with oxygen : this is the phenome- non of flame. But fire and flame are not necessary concomitants of the union of bodies with oxygen. It is true that such union is always accompanied by the production of heat ; but often this heat is not luminous ; sometimes it is imperceptible to our senses. Thus iron, the combination of which with oxygen at a red heat gives rise to such a brilliant combustion, may unite with this gas at ordinary temperatures under the influence of moisture. There is thus formed ferric hydrate, which consti- tutes rust. This oxidation of the iron, which takes place slowly, pro- duces a feeble disengagement of heat, which is, however, imme- diately dissipated. Such phenomena of oxidation are designated by the name slow combustion. The term combustion would then be synonymous with oxi- dation did we not know, on the other hand, that all chemical combination gives rise to the production of heat. If copper be thrown into boiling sulphur, a vivid incandescence is pro- duced, due to the union of the two bodies. Likewise antimony and arsenic, when projected in fine powder into an atmosphere of chlorine, unite with the latter body, producing a brilliant combustion. It is seen that in these cases the production of luminous heat indicates an energetic combination, but not an oxidation. Oxygen is one of the elements of the air ; it is the cause and the agent of all combustion, of all oxidation which takes place in our atmosphere ; and the oxygen fixes itself upon OXYGEN. 59 burning bodies in such a manner that the product of the com- bustion contains all of the matter of the combustible body and all of the matter of the oxygen. This is one of the fundamental truths of chemistry, and for its discovery not less than a cen- tury and a half of work was required. The glory of the dis- covery belongs to Lavoisier. His researches on combustion revealed to him the true nature of the phenomena of respiration. The respiration of animals is a slow combustion ; it is the source of animal heat. It gives rise to the formation of carbonic acid gas and water, products of the complete oxidation through which must pass those organic matters in the economy which no longer serve the purposes of life, and all of which contain carbon and hy- drogen. The production of carbonic acid gas by the act of respira- tion is easy to prove. It is only necessary to blow, by the aid of a tube, the air contained in the lungs through clear lime- water, which soon becomes milky from the formation of insolu- ble carbonate of lime. An annular jet of hydrogen through which a jet of oxygen is forced constitutes what is known as the oxyhydrogen blow- pipe, and is one of the most intense sources of heat known. Platinum melts before it like wax, and iron and other combus- tible metals burn brilliantly when introduced into its flame. The flame of the oxyhydrogen blowpipe gives but little light, but when it is projected upon a piece of lime, the latter becomes heated to dazzling incandescence, constituting the Drummond or calcium light. OZONE, OR OXYGEN PEROXIDE. OO 2 . The repeated discharges of a good electric machine develop a peculiar odor. This is due to the production of a body which was discovered by Schbnbein in 1840, and which he named ozone (from oo>, I smell). Experiment. Some potassium permanganate is mixed with barium dioxide in a mortar, the mixture transferred to a flask, and moistened with sulphuric acid. The characteristic odor of ozone immediately becomes perceptible, and a moistened paper, impregnated with potassium iodide and starch and held in the 60 ELEMENTS OF MODERN CHEMISTRY. neck of the flask, immediately assumes a blue color. 1 This effect is caused by the ozone evolved. This remarkable body is also formed under the following circumstances. 1 . By the passage of electric sparks through oxygen. It is sufficient to pass a series of electric sparks through oxygen contained in a tube above a solu- tion of iodide of potassium and starch, in order to produce the blue color caused by the ozone (Fig. 20). It has been noticed that the largest quantity of ozone is pro- duced when the passage of the electricity through oxygen is ef- fected, not by sparks, but by non- luminous or obscure discharges (Andrews and Tait, de Babo). Dry and pure oxygen can be con- verted into ozone in this manner. But this conversion only takes place partially, the ozone formed remaining mixed with a large excess of oxygen. A contraction takes place at the moment the oxygen is transformed into ozone. These experiments prove that ozone is condensed oxygen (Andrews and Tait, de Babo, Soret). 2. By the electrolysis of water. When acidulated water is decomposed by the battery current, the oxygen which is disengaged at the positive pole contains small quantities of ozone, and the proportion of the latter may be increased by adding a considerable quantity of sulphuric or chromic acid to the water. 3. During slow oxidation. Some sticks of cleanly-scraped 1 Such a paper is called ozonoscopic. It is colored blue by the combina- tion of the starch with the iodine set at liberty by the ozone. According to Houzeau, it is preferable to use a delicate, wine-colored litmus-paper, one-half of which is impregnated with potassium iodide. Ozone will change the color of this half to blue, for, in decomposing the potassium iodide, it forms potassium hydrate, and this restores the blue color to the litmus. Under these conditions, the other half of the paper undergoes no change in color, while it would be colored red by acid vapors, or blue by ammonia. FIG. 20. OZONE. 61 phosphorus are introduced into a bottle containing enough water to just about half immerse them, and the whole is agi- tated from time to time. In a short time the air in the bottle will be charged with a small quantity of ozone. According to Schonbein, who observed these facts, ozone is produced during all slow combustions. Thus, when oil of tur- pentine is exposed to the air under the influence of sunlight, it is slowly oxidized, and in becoming resinified, it becomes at the same time charged with a small quantity of ozone, which dissolves in it. 4. JBy the decomposition of barium dioxide by sulphuric acid. This decomposition gives rise to barium sulphate and oxygen charged with a small quantity of ozone (Houzeau). H*S0 4 BaO 2 = BaSO* + H 2 + The barium dioxide is introduced in small portions into sul- phuric acid contained in a flask, to the neck of which is fitted a glass stopper pierced for the passage of the delivery-tube, which is ground in (Fig. 21). FIG. 21. Properties of Ozone. Ozone possesses an intense and pecu- liar odor. At a temperature of 290 it is reconverted into ordinary oxygen, the volume of which is greater than that occupied by the ozone. It is then certainly condensed oxygen. It has energetic oxidizing properties ; it even oxidizes bodies which possess only feeble affinities for oxygen. In the presence of alkalies it combines with nitrogen, converting it into nitric acid, which combines with the alkali. It oxidizes silver at ordinary temperatures, converting it into 6 62 ELEMENTS OF MODERN CHEMISTRY. the dioxide Ag 2 2 . It instantly decomposes potassium iodide, setting free the iodine. It is insoluble in water, but is entirely soluble in oil of turpentine and oil of cinnamon, both of which it slowly oxidizes. It oxidizes and destroys the greater number of organic substances. In most of these oxidations only a third part of the oxygen contained in ozone is active ; the other two- thirds become free in the form of ordinary oxygen, so that the volume of the latter set free is exactly equal to that primitively occupied by the ozone. Hence it is concluded that 3 volumes of oxygen are con- densed into 2 volumes by their conversion into ozone, and if ordinary oxygen be the oxide of oxygen 00, ozone will be oxy- gen peroxide OO 2 (Odling). 00 = 2 volumes of oxygen. OO 2 or / \ = 2 volumes of ozone. 00 This conclusion of Odling's concerning the nature of ozone, has been verified by the determination of the density of this body. Soret has established that when ozone diluted with oxy- gen is absorbed by oil of turpentine or oil of cinnamon, there is a diminution of volume sensibly double the increase of volume noticed on subjecting the same gas to the action of heat. He naturally concludes that the density of ozone is one and a half times that of oxygen, or 1.658. These figures have been confirmed by direct experiments upon the rapidity of diffusion of ozone. It has been shown by the researches of Graham that when diffusion between two gases takes place through an opening, without the interposition of a diaphragm, the rapidity of diffusion is inversely as the square roots of the densities of the gases. Soret has demonstrated that the rapidity of diffusion of ozone is notably greater than that of chlorine, and very near but somewhat less than that of car- bonic acid. It results that its density is less than that of chlorine, and a little greater than that of carbonic acid, which is 1.525 ; this confirms the density 1.658. An important property of ozone is its reduction by hydrogen dioxide, and the simultaneous decomposition of the latter com- pound. The products are ordinary oxygen and water. OO 2 4- H 2 2 = 2(OO) + H 2 Ozone. Hydrogen dioxide. Ordinary oxygen. Water. THE ATMOSPHERE. 63 ATMOSPHERIC AIR. The air is a mixture of oxygen and nitrogen. It also con- tains traces of carbonic acid gas and a variable proportion of vapor of water. Its composition was established by Lavoisier by an experi- ment that has become celebrated. Having heated mercury in a limited quantity of air to a temperature near its boiling-point for several days, he observed the formation of a red powder, a combination of the mercury with oxygen. On the termination of the experiment, he found that the volume of the air had diminished about one-sixth. He carefully collected the oxide formed, introduced it into a small retort, and heated it to red- ness. He thus obtained a gas " eminently qualified to support combustion and respiration," and the volume of which was sensibly equal to that of the gas that had disappeared. This gas he named oxygen. He mixed it with the irrespirable resi- due from the first experiment, which would not support com- bustion, and so reconstituted atmospheric air. The composition of the latter was thus established by analysis and synthesis. This experiment was infinitely more instructive than that undertaken by Scheele at about the same time. The great Swedish chemist only absorbed the oxygen of the air by the alkaline sulphides. The nitro- gen remained as residue, but the oxygen combined with the sulphide could not be again separated. However, neither one nor the other of these methods could give the exact propor- tion according to which the oxygen and nitrogen are mixed in the atmosphere. This has been deduced from the follow- J?IQ. 22. ing experiments. Experiments. 1. Into a small bent tube closed at the upper end, filled with mercury and inverted in a vessel of the same metal, are passed 100 volumes of air (Fig. 22). A small piece of phosphorus is then introduced and brought into the upper limb, where it is heated by the aid of a spirit- lamp. It takes fire, and in burning consumes all of the 64 ELEMENTS OF MODERN CHEMISTRY. oxygen of the 100 volumes of air. The operation has termi- nated when the flame of the phosphorus vapor has extended down to the column of mercury. The residual gas is then allowed to cool, and on being measured is found to be reduced to 79 volumes. It is nitrogen. 2. The absorption of oxygen by phosphorus will take place in the cold, if a long stick of this substance be in- troduced into a determined volume of air contained in a graduated tube. The experiment requires several hours, and gives the same result as the preceding. 3. 100 volumes of air are measured into a graduated tube on the mercury-trough. A concentrated solution of potassium hydrate is introduced, and then some pyro- gallic acid, a white, crystalline substance employed in photography; the whole is then rapidly agitated, the extremity of the tube being closed by the thumb. The alkaline solution is immediately blackened by the destruction of the pyrogallic acid. All of the oxygen is rapidly absorbed, and when the tube is opened, under the surface of the mercury, the 100 volumes of air are found reduced to about 79 volumes. FIG. 23. FIG. 24. 4. There is another method capable of still greater precision : Fig. 23 represents a Bunsen's eudiometer ; it is a stout glass tube about 60 centimetres long and 2 centimetres in diameter. Two platinum wires are hermetically sealed into the upper ex- tremity through the whole thickness of the glass. Each ter- THE ATMOSPHERE. 65 minates exteriorly in a small loop, and on the interior follows the curve of the end nearly to the centre, so as to leave an interval of about 1 centimetre between the extremities of the two wires. The tube is graduated in millimetres, and the ca- pacity of each division is known. It is filled with mercury and inverted upon a small trough. 100 volumes of air and 100 volumes of hydrogen are then introduced. One of the plati- num loops is then put into communication with an electrical conductor, and the other with the earth, and a spark is passed through the mixture (Fig. 24). A flash appears in the tube, and all of the oxygen of the 100 volumes of air has combined with hydrogen to form water. There thus results a vacuum, which is filled by the mercury, and in place of 200 volumes of gas introduced into the eudiometer, we find, all corrections being made, only 137.21 volumes of a mixture of hydrogen and nitrogen. 62.79 volumes have then disappeared to form water, and this water contains all of the oxygen contained in 100 volumes of air ; as each volume of this oxygen must consume 2 vol- umes of hydrogen, it follows that the 62.79 volumes which have disappeared must have contained 20.93 volumes of oxygen and 41.86 volumes of hydrogen. Hence the 100 volumes of air introduced into the eudiom- eter contained 20.93 volumes of oxygen and 79.07 volumes of nitrogen. Such is the composition of the air by volume. As nitrogen is lighter than oxygen, these volumetric relations do not express the composition of the air by weight. This was determined very exactly by Dumas and Boussingault in the following manner. A globe, A (Fig. 25), having a capacity of 15 or 20 litres, and fitted with a brass cap and stop-cock, R", by which it may be connected with an air-pump, is joined "to a hard glass tube, BB', having a stop-cock at each end, R and R', and filled with metallic copper. The air is exhausted from the globe and tube, and the weight of each is then accurately determined. The tube BB' is placed in a combustion-furnace, and by its extremity B' is connected with the tubes K, I, H, G, F, E, D, C. The tube with bulbs C contains a solution of caustic po- tassa ; the tubes D and E are filled with pumice-stone impreg- nated with caustic potassa, and the tubes F and G with frag- ments of solid caustic potassa ; the bulbs H contain sulphuric 6* 66 ELEMENTS OF MODERN CHEMISTRY. acid, and the last tubes, I and K, are filled with fragments of pumice-stone saturated with sulphuric acid. The potassa serves to remove from the air the small quantity of carbonic acid gas which it contains, and the sul- phuric acid absorbs the moisture. The tube filled with copper is now heated to redness, its stop-cocks being open, and the stop-cock of the globe is gradually opened. Air immediately enters, but it is first obliged to tra- verse the series of tubes, where it is deprived of its carbonic acid gas and vapor of water, and also the tube filled with incandescent cop- per, which absorbs the oxygen. It is then pure nitrogen which enters the globe. The experi- ment has terminated when the tension of the gas in the globe is equal to the exterior pressure, that is, when no more air enters. The stop- cock R," is now closed. The tube and globe are allowed to cool, and are weighed separately. The increase in weight of the globe gives the weight of the nitrogen which has entered. The increase in weight of the tube, which was first weighed exhausted of air, gives the weight of the oxygen which has THE ATMOSPHERE. 67 combined with the copper, plus the weight of the nitrogen remaining in the tube at the close of the experiment. The weight of this nitrogen is determined by exhausting the tube and weighing a third time. The difference between the second and third weighings indicates the weight of the nitrogen re- maining in the tube at the end of the experiment, and this weight added to that of the nitrogen contained in the globe constitutes the total weight of nitrogen in the air analyzed. The weight of the oxygen is given by the difference between the third and first weighings of the tube. By this method Dumas and Boussingault found that 100 parts of air contain by weight Oxygen 23.13 Nitrogen 76.87 These two gases are simply mixed in the air ; they do not exist there in a state of combination ; and the proportions of the mixture are universally the same with very slight varia- tions. At the summits of the highest mountains, at the centres of the continents, and over the vast expanse of the seas, the air has been shown to be nearly equally rich in oxygen. From a comparison of a great number of analyses, Regnault has es- tablished that as a rule the percentage of oxygen only varies from 20.9 to 21.0 ; air which has been collected on the open sea and close to the surface of the water, has been found to contain a somewhat smaller amount (20.6), a circumstance which may be attributed to the dissolving action of the water. Nitrogen and oxygen are by far the most abundant con- stituents of the atmosphere ; among the substances which are contained in small proportion must be mentioned particularly carbonic acid gas and vapor of water. Carbonic Acid Gas and Vapor of Water. If lime-water be poured into a flat dish and exposed to the air, in a few hours its surface will be found covered with a white pellicle formed of little crystals of calcium carbonate. This experiment demonstrates the presence of carbonic acid gas in the atmosphere. The watery vapor may be condensed by exposing to the air a glass vessel containing a mixture of ice and salt. The sides of the vessel soon become covered with a layer of frost, resulting from the solidification of the water which has been condensed from the air by the cool surface of the glass. The exact quantities of carbonic acid gas and vapor of water ELEMENTS OF MODERN CHEMISTRY. contained in the air may be determined by drawing the latter through tubes containing sulphuric acid and caustic potassa. The aspiration is obtained by means of a bottle or a tin vessel, V (Fig. 26), filled with water. On opening the stop-cock r, Fia. 26. the water runs out, and air is drawn in through the tubes F and E, filled with fragments of pumice-stone wetted with sul- phuric acid, then through D and C, containing pumice-stone impregnated with caustic potassa, and finally B, which is like the first two. These tubes increase in weight from the absorp- tion of vapor of water in the first two, and carbonic acid in the others. The difference in weight of the tubes F and E before and after the experiment gives the proportion of con- densed water ; the difference of D, C, and B gives the propor- tion of carbonic acid gas. The volume of air is equal to that of the water which has run out of the aspirator. According to the experiments of Theodore de Saussure, the quantity of carbonic acid gas contained in the air varies from 4 to 6 ten-thousandths. It is increased in inhabited places. It is greater at night than during the day, a circumstance that must be attributed to the influence of vegetation. It is dimin- THE ATMOSPHERE. 69 ished after a rain, and is found in its minimum proportion above the surface of large lakes. The sources of this carbonic acid gas are various. In cer- tain regions fissures in the earth disengage large volumes ; vol- canoes emit immense quantities ; certain spring waters are supersaturated, and disengage it in abundance when they reach the surface of the earth. But the greater portion is produced by the phenomena of combustion which take place on the earth's surface ; and among these phenomena must be included respiration, which is a slow combustion. Experiment. If by the aid of a glass tube, a (Fig. 27), air from the lungs be blown through lime-water, the latter becomes clouded, by the formation of calcium carbonate. The carbonic acid gas thus fixed by the lime comes from the respiration, which is an abundant source of that gas. Does carbonic acid gas accumulate indefinitely in the atmosphere ? No. Re- jected and excreted by ani- mals, it serves for the res- piration of plants. The green parts of vegetables possess the power of de- composing this gas under the influence of the sun's light. The carbon is fixed, JT IG 27. and serves for the nu- trition of the plant ; the oxygen is rejected, if not wholly, at least in great part. This truth is one of the most important achievements of the science of the last century. It is due to the successive labors of Priestley, Bonnet, Ingenhouz, Senne- bier, and Theodore de Saussure. Independently of carbonic acid gas and vapor of water, air contains other matters mixed with or. suspended in it in very small quantities. Among these must be mentioned : 1. Traces of ammonia, or rather of ammonium carbonate. These substances are dissolved by rain-water, and play an important part in vegetation. 70 ELEMENTS OF MODERN CHEMISTRY. 2. A trace of hydrogen carbide (Boussingault). 3. A small quantity of nitric acid in the form of ammonium nitrate. It is supposed that nitric acid is formed in the air by the direct union of the nitrogen and oxygen under the influ- ence of atmospheric electricity. Schbnbein asserts that the air contains traces of ammonium nitrite : (NH*)N0 2 4. A body which possesses the property of imparting a blue color to papers saturated with starch and potassium iodide. It is held, and not without reason, that this substance is ozone. The phenomenon would also be caused by the presence of traces of nitrous vapors or chlorine in the air ; but Andrews has shown that air contains a principle which decomposes po- tassium iodide, and loses this property when it is brought to a high temperature. This fact can be explained if the air con- tain ozone, which is destroyed by heat ; it cannot be explained if it contain chlorine or nitrous vapors. Besides, the air con- tains only very slight traces of ozone, which vary greatly ; often none is present. The relative proportion of ozone pres- ent is approximately estimated by the greater or less intensity of the blue color produced upon ozonoscopic paper. 5. Solid particles suspended in the air and carried to a dis- tance by the winds. In perfectly calm air these corpuscles are deposited, forming a dust of which the composition is very variable. It contains various microscopic vegetable and animal germs (Pasteur). WATER. Vapor density compared to air 0.623. Vapor density compared to hydrogen * . . . 9. Molecular weight H 2 = 18. Water is the product of the combination of hydrogen and oxygen ; its composition was established by Lavoisier in 1785. 1 The density of vapor of water compared to that of hydrogen is 9 ; that is, if the weight of 1 volume of hydrogen be represented by 1, the weight of 1 volume of vapor of water will be 9 ; in other words, vapor of water is nine times more dense than hydrogen under the same conditions of tem- perature and pressure. 2 The weight of the molecule or the molecular weight expresses the weight of 2 volumes of vapor, if the weight of 1 volume of hydrogen be represented by 1. WATER. The combination takes place exactly in the ratio of 2 volumes of hydrogen to 1 volume of oxygen, as demonstrated by the following experiments. 1. Analysis of Water by Electrolysis. Water slightly acid- ulated with sulphuric acid is introduced into the vessel C (Fig. 28), through the bottom of which rise two platinum wires. These wires are hermetically sealed in the walls of the glass, and the free exterior ex- tremities are con- nected with the poles of a galvanic battery. The cur- rent passing through the acidulated liquid decomposes the Fio 28. water, 1 and bubbles of gas are formed and rapidly rise from the two platinum wires which constitute the poles. If two small tubes filled with water be inverted over these wires, the gases may be collected, aud it will be found that the gas disengaged at the negative pole is sensibly double in volume that disengaged at the posi- tive. The first is hydrogen, and the second oxygen, and the proportion in which these gases ape set free would be exactly that of 2 to 1, were it not that a small quantity of oxygen re- mains dissolved in the acid liquid, or, under certain condi- tions, combines with a portion of the water surrounding the negative pole to form a trace of hydrogen dioxide, as will be mentioned farther on. This experiment of the decomposition of water by the pile was made for the first time, in 1801, by two English physi- cists, Nicholson and Carlisle. 1 Under these conditions, it is really the sulphuric acid which is decom- posed; H 2 SO* breaks up into H 2 , which is liberated at the negative pole, and SO 4 , which separates at the positive pole, and is at once decomposed into SO 3 and 0. The is disengaged, and the SO 3 in the presence of the water becomes again hydrated, reforming sulphuric acid. SO 3 + H 2 == H 2 SO*. The electrolytic action is thus confined to the sulphuric acid, which alone is decomposed. *T2 ELEMENTS OF MODERN CHEMISTRY. 2. Eudiometric Synthesis. The composition of water can be established by synthesis, that is, by the combination of the two elements, hydrogen and oxygen. The experiment, which is made in an eudiometer, has already been described (page 28). It demonstrates that the two gases combine in the exact ratio of 2 volumes of the first to 1 of the second, and that these 3 volumes of gas are condensed into 2 volumes of vapor of water. These experiments establish the volumetric composition of water ; its composition by weight can be deduced from them, the densities of hydrogen and oxygen being known ; for the weighable matter of 2 volumes of hydrogen being added to the weighable matter of 1 volume of oxygen, it is only necessary to add twice the weight of 1 volume of hydrogen to the weight of 1 volume of oxygen in order to determine the weight of 2 volumes of vapor of water. That is to say, the ratio by weight in which hydrogen combines with oxygen to form water is that of double the density of hydrogen (the weight of 2 volumes of H) to the density of oxygen (the weight of 1 volume of 0). This ratio is 2 X 0.0693 _ 0.1386 _ 1 1.1056~ ~ 1.1056 ~8 It may be deduced in a more simple manner by a com- parison of the densities of hydrogen and oxygen. If 1 volume of hydrogen weighs 1, 1 volume of oxygen weighs 16 ; the weight of 2 volumes of hydrogen will then be 2, and it will be seen that the two gases unite, by weight, in the ratio of 11 16~8 18 grammes of water then contain 16 grammes of oxygen and 2 grammes of hydrogen. This composition, which can be determined only in an approximative manner by a compari- son of the densities, owing to the difficulties in the methods of weighing gases, has been established in the most rigorous manner by Dumas, in an experiment which has become classic, and will now be described. 3. Synthesis of Water by the Gravimetric Method. In order to determine the composition of water by synthesis it is suffi- cient to combine an indeterminate quantity of hydrogen with a precisely determined weight of oxygen, and to weigh exactly the water formed. By subtracting from this latter weight that WATER. of the oxygen contained in the water, the weight of the hydro- gen which has com- bined with that oxy- gen is obtained. In order to thus combine hydrogen with oxygen, it is convenient to make the former gas react upon an oxidized body which will read- ily yield its oxygen to the combustible gas. Cupric oxide, or black oxide of cop- per, CuO, first sug- gested by Gray-Lus- sac, and employed for this purpose by Ber- zelius and Dulong, fulfils these condi- tions. Although un- decomposable by heat alone, it is readily re- duced by hydrogen when heated in an at- mosphere of that gas. Dumas employed the apparatus represent- ed in Fig. 29. Hydrogen is pre- pared by the action of dilute sulphuric acid upon zinc, and is purified by being conducted through a series of U tubes, the first containing frag- ments of glass wet with a solution of lead acetate, the second, fragments of glass wet with a solution of silver sulphate, and 74 ELEMENTS OF MODERN CHEMISTRY. the third, pumice-stone, impregnated with caustic potassa. The lead acetate retains hydrogen sulphide ; the silver sulphate absorbs hydrogen arsenide, and the potassa absorbs any traces of carbides of hydrogen. The hydrogen thus purified is dried by passage through an- other series of U tubes, the first containing calcium chloride, and the others pumice-stone saturated with sulphuric acid. The latter tubes are cooled by being surrounded with ice. The gas is lastly passed through a smaller tube containing phosphoric oxide. The weight of this tube must remain constant during the whole of the experiment. It is called the witness-tube. The pure and dry hydrogen now passes through a green glass bulb, which contains pure cupric oxide. The weight of this bulb, together with the oxide which it contains, is deter- mined with care. The receiver B', as well as the U tubes which terminate the apparatus, are also accurately weighed. When the whole of the air contained in the apparatus has been expelled by the hydrogen, the flask is heated and the cupric oxide is reduced. Water is formed and is in great part condensed in the liquid state in the receiver, but a portion of the vapor remains uncondensed and is carried off by the excess of hydrogen. This vapor is retained in the second series of U tubes, which contain calcium chloride and pumice-stone satu- rated with sulphuric acid. When the reduction has almost terminated, the bulb is allowed to cool, the current of hydro- gen being continued ; this gas is finally displaced by a current of air, and the weighings are then made. The weight of the bulb has decreased by that of all of the oxygen which has been taken from the oxide of copper by the hydrogen, and which now exists in the water formed. The weight of the receiver and the condensing apparatus con- nected with it is increased by the weight of all the water formed. By subtracting the weight of the oxygen from that of the water we find the weight of the hydrogen. By the aid of this rigorous method Dumas has found that 100 parts by weight of water contain Hydrogen 11.11 Oxygen 88.89 100.00 These numbers are in the exact ratio of Hydrogen 1 Oxygen . . . 8 WATER. 75 Physical Properties. Pure water has neither taste nor odor. It is limpid and colorless. It occurs in three states in nature ; during the colds of winter it is solid. Ice, snow, frost, sleet, and hail are the different forms which it assumes in this state. The temperature at which ice melts is one of the stand- ard points in the thermometric scale. To this temperature corresponds the of the centigrade scale, which is adopted in this work. Snow is composed of an agglomeration of little crystals; these are hexagonal prisms, which often present the forms rep- resented in Fig. 30. FIG. 30. At the moment of freezing, water expands, and its density is then less than that which it possesses in the liquid state. The density of ice is 0.93. Water contracts in volume from to -f 4, and presents its maximum density at the latter tem- perature. Its density at this point is chosen as the unit of comparison for the densities of solid and liquid bodies. Water and even ice are continually emitting invisible vapors which mix with the air, and are, as it were, dissolved in it. This vaporization takes place more actively as the temperature is raised. The air is said to be saturated with vapor at any given tem- perature when it refuses to take up any more vapor at that temperature. Under these conditions, if the temperature be lowered, a portion of the vapor is condensed in fine drops, which remain suspended in the air in the form of mist or visi- ble vapor. The point at which the moisture of the air is con- densed is called the dew-point. Water begins to boil when its vapor acquires sufficient ten- sion to overcome the atmospheric pressure. This is the boil- ing-point, and under a pressure of 0.760 metre corresponds to 100 of the centigrade scale. 76 ELEMENTS OF MODERN CHEMISTRY. Chemical Properties. Water is partially decomposed by the highest temperatures at our command. On pouring melted platinum into an iron mortar containing water, Grove observed a disengagement of bubbles composed of an explosive mixture of oxygen and hydrogen. According to H. Sainte-Claire De- ville, vapor of water undergoes a partial decomposition, which he calls dissociation, when exposed to a temperature between 1100 and 1200. In order to collect the gases resulting from this decomposition it is necessary to separate them before they have reached a part of the apparatus where a less elevated temperature would permit their recombination. For this pur- pose Deville directed a current of steam through a porous clay tube, a (Fig. 31), surrounded by a tube of glazed porcelain, b, FIG. 31. which was heated to whiteness in a powerful furnace. A cur- rent of carbonic acid gas was passed through the annular space between the two tubes, by means of the tube c. The vapor of water was decomposed by the heat into hydrogen and oxygen ; but these two gases separated from each other : the hydrogen, being the more diffusible, passed in great part through the porous tube, while the oxygen was delivered by the interior tube, together with a small quantity of carbonic acid gas, which entered by diffusion. The gases evolved by the two tubes were collected in a small jar filled with a solution of caustic potassa by which the carbonic acid gas was absorbed, and there re- mained an explosive mixture of hydrogen and oxygen. Water is decomposed by an electric current, as already seen. WATER. 77 It is likewise decomposed by many of the elements, metallic and non-metallic, which combine with one or the other of its component elements. Thus, chlorine decomposes it at a red heat, uniting with the hydrogen to form hydrochloric acid, and setting free the oxygen ; also under the influence of light at ordinary temperatures. A number of the metals decompose water, liberating the hydrogen. Iron decomposes it at a red heat, taking up the oxygen and setting free the hydrogen ; potassium and sodium, as we have seen in the case of the latter metal, produce the same effect at ordinary temperatures. Many compound bodies seize upon the elements of water, and are decomposed by it. Such are the chlorides of phos- phorus and antimony. In these reactions, which will be studied farther on, the hydrogen of the decomposed water unites with the chlorine, the oxygen with the other element. We have already noticed the action of water upon the non- metallic and metallic oxides. It combines with many of these compounds, forming either acids or metallic hydrates. Certain of these reactions are worthy of reconsideration. It is especially important to fully appreciate the part played by the water which enters into them. When potassium oxide becomes hydrated to form caustic potassa, the reaction takes place by a double decomposition, which may be expressed by the following equation : a)l} + 1} = Potassium oxide. Water. Potassium hydrate. Potassium hydrate. It will be seen that both the potassium oxide and the water are converted into potassium hydrate by the exchange of an atom of potassium for an atom of hydrogen. Potassium hydrate is, as it were, derived from water by the substitution of an atom of potassium for an atom of hydrogen. This substitution takes place directly when water is decomposed by potassium. (2) 2H 2 -f K 2 = 2KOH + H 2 The potassium hydrate in its turn may lose the remaining atom of hydrogen ; if it be heated with potassium, this hydro- gen is displaced, and potassium oxide is formed. (3) 2KOH + K 2 = 2K 2 O + H 2 Potassium hydrate. Potassium. Potassium oxide. Hydrogen. 78 ELEMENTS OF MODERN CHEMISTRY. It will be seen from what precedes that, starting with water, we may form potassium hydrate (2), potassium oxide (3), and this again may be converted into potassium hydrate (1). The three compounds are then closely related. Each contains 1 atom of oxygen combined with 2 atoms of another body, hy- drogen or potassium, and the relation is clearly expressed in the following formulae : 1} Water. Potassium hydrate. Potassium oxide. If hypochlorous oxide, CPO, be poured into water, it is in- stantly dissolved and converted into hypochlorous acid. The reaction is expressed in the following equation : cn n H| O H ) cii n Cl } C + H I C Cl I C + H J | C Hypochlorous oxide. Water. Hypochlorous acid. Hypochlorous acid. Both the hypochlorous oxide and the water are converted into hypochlorous acid by the exchange of an atom of hydro- gen for an atom of chlorine, so that the hypochlorous acid may be said to represent water in which 1 atom of chlorine is substituted for an atom of hydrogen. Thus, by their atomic constitution both potassium hydrate and hypochlorous acid are closely related to water. But on comparing them together they are found to differ widely in their properties, both from each other and from water itself. How could it be otherwise with bodies containing elements as unlike as potassium and chlorine ? Indeed, the distance which separates potassium hydrate and hypochlorous acid is not greater than that which separates potassium and chlorine. Thus, a difference of elements may imply a marked difference of properties between bodies which otherwise present a similar con- stitution, and which may be said to belong to the same type. Water is one of these types. Its constitution serves as a sort of model for that of a multitude of compounds. It will be sufficient to reconsider the examples already cited, and we may say that water, potassium hydrate, potassium oxide, hypochlo- rous acid, and hypochlorous oxide belong to the water type. . ) Cl) HJ p H P HP Cl Ci Hypochloroua Hypochlorous Water. Potassium Potassium oxide. acid. hydrate. oxide. WATER. 79 The preceding considerations give but a limited idea, but one sufficient for the present, of the role played by water in chemical phenomena. This role is one of great importance, for water takes part in an immense number of reactions, either by its decomposition, its formation, or its combination. Water presents still another mode of action. It dissolves very many bodies, and this solvent action is exerted upon gases, liquids, and solids. Solvent Properties of Water. When a gas dissolves in water, it changes its state, it becomes itself liquid, and in lique- fying it evolves heat. In the same manner a solid body be- comes liquid by the act of solution, but in order to become liquid it must absorb heat. Consequently, the solution of a gas in water takes place with a production of heat ; that of a solid body takes place with a lowering of temperature, or, to use a common expression, a production of cold. But sometimes this physical phenomenon of the solution of a solid body in water, that is, its liquefaction and diffusion in the liquid, is complicated by a chemical action. Experiment. If water be poured upon fused and powdered calcium chloride, the salt is instantly dissolved with a produc- tion of heat. This heat is the evidence of a chemical com- bination, and the water has indeed combined with the calcium chloride ; if now the solution be sufficiently evaporated, it will deposit fine transparent crystals of hydrated calcium chloride. The water contained in these crystals, and which is necessary for their formation, is what is called water of crystallization. It is contained in definite proportions, and is retained in the crystals by affinity. For this reason the combination of water with calcium chloride is accompanied by a production of heat. If these crystals of calcium chloride be dissolved in water, they disappear, and the temperature of the liquid is depressed. The physical phenomenon of the solution of a solid body in water can thus be separated from the chemical phenomenon of its combination with that liquid. Natural State of Water. Water is not met with in a pure state in nature. Whether it has rested upon or has flowed over the surface of the soil, whether it has fallen in the form of rain, mist, or dew, or whether it has just issued from its subterranean passages, it always contains various matters in solution. It takes up the gases from the atmosphere, and also certain bodies which it there finds suspended or in vapor. On the 80 ELEMENTS OF MODERN CHEMISTRY. surface or in the bosom of the earth it dissolves the soluble substances which it encounters. Hence the composition of natural water presents great variations, according to the origin of the water and the localities where it has collected, or the soils through which it has travelled. In general, meteoric waters, that is, those which result from the condensation of the aqueous vapor diffused through the atmosphere, are more pure than those which have collected upon the earth's surface. The latter present in their physical and chemical properties, in their composition, and in their action upon the animal econ- omy, such differences that they are classified in several groups. Soft or potable waters are distinguished from hard waters. The first are such as hold only small quantities of foreign mat- ters in solution, and are essentially fit for domestic use. The second are too highly charged with saline matters, and princi- pally the salts of calcium, to be fit for such purposes. Good potable water should be cool, limpid, without odor, should have a faint but agreeable taste, which should be neither insipid, saline, nor sweet, and should cook and soften vegetables and dissolve soap. The purest water is not necessarily the best. Thus distilled water, rain-water, and that coming from the melting of ice and snow, although more pure, are less salubrious than good spring or river water. Good potable water should be aerated, that is, it should hold in solution the gases contained in the atmosphere : oxygen, nitrogen, and carbonic acid. Rain-water takes from the atmos- phere a proportion of oxygen, and especially of carbonic acid gas, much greater than that in which these gases are contained in the air. This must be so, for Dalton has shown that the solvent action of water upon a gaseous mixture is measured for each gas by the product of its coefficient of solubility and the figure expressing the proportion of that gas in the mixture. These gases are driven out of water by boiling. The following figures give the proportions of the atmospheric gases expelled by boiling from a litre of water from the Seine, in the month of January, and also the proportions contained in a litre of rain-water (Peligot) : Water of the Seine. Rain-Water. Carbonic acid gas . . 22.6 cubic centimetres. 0.5 c. c. 1.77 Nitrogen 21.4 15.1 64.47 Oxygen 10.1 7.4 33.76 54.1 23.0 100.00 WATER. 81 It is seen that the running water contains a larger amount of all of the gases than rain-water, and a notably larger pro- portion of carbonic acid. Solid Matters dissolved in Water. Soft waters generally contain a small proportion of fixed matters, among which are certain salts of calcium and magnesium, certain alkaline salts, silica, and organic matters. The calcium salts are the carbonate and sulphate, and some- times traces of the chloride, nitrate, and phosphate. Calcium carbonate, or carbonate of lime, is almost insoluble in pure water, but dissolves readily in water charged with carbonic acid gas ; in such solutions it exists as dicarbonate. When water thus charged with calcium dicarbonate is boiled, that salt is decomposed, carbonic acid gas is disengaged, and neutral calcium carbonate is precipitated. 'When the propor- tion of calcium dicarbonate contained in spring-water is large, it may happen that as the water loses carbonic acid gas the calcium carbonate is deposited at ordinary, temperatures. This effect is favored by the tumultuous movements to which spring- water is subjected either in flowing over an inclined bed or in conducting-pipes. The carbonate then forms a crystalline de- posit, which incrusts the interior walls of the pipes and, in general, whatever objects may be plunged into such waters, which for this reason are called incrusting or petrifying waters. The presence of small quantities of calcium dicarbonate in drinking-water may be considered as a good condition, from a hygienic stand-point, for the system needs calcareous salts for the development and nutrition of the bony structures. Calcium sulphate, or sulphate of lime, exists in solution in many waters, especially in spring and well waters. When the proportion does not exceed fifteen or twenty centigrammes per litre, such water may be used without inconvenience for do- mestic purposes. Water largely charged with calcium sulphate is called selenitous water ; it does not become clouded on ebul- lition. Like all other strongly calcareous water, it does not dis- solve soap without first forming a flocculent precipitate. Salts of barium produce with such water an abundant white precipi- tate of barium sulphate, which is insoluble in nitric acid. Such water is unfit for economic purposes. In general, the proportion of calcareous salts in potable water should not exceed five or six decigrammes per litre ; water D* 82 ELEMENTS OF MODERN CHEMISTRY. containing more than this is difficult to digest, and is called hard water. Mineral or Medicinal Waters. These are waters that by virtue of their temperature or chemical constituents exercise a special action upon the animal economy, and consequently have a therapeutic value. They are cold or warm. They are called warm when their temperature at the moment of emergence is above 12 or 15. Of course their temperatures vary greatly, covering the whole thermometric scale from 25 to 100. There are numerous hot springs in California, Colorado, and Virginia. The tempera- ture of the Grand Geyser in Iceland is even above 100 in the depths of the tube from which it issues. According to their chemical constituents, mineral waters are classified in a number of characteristic groups, distinguished either by the predomi- nance of certain constituents, or by the presence of principles particularly active. These groups are as follows : Acidulous or gaseous waters, characterized by the presence of free carbonic acid. Alkaline waters, characterized by the presence of a greater or less proportion of sodium dicarbonate, or of an alkaline silicate. Chalybeate waters, holding a salt of iron in solution. Saline waters, or those containing certain neutral salts. Sulphur waters, characterized by the presence of hydrogen sulphide or other soluble sulphide. On arriving at the surface of the earth, certain of these mineral waters undergo a change in chemical constitution. Such are the sulphur waters which absorb oxygen, as will be noticed presently. Those containing free carbonic acid lose a part of their gas, and it often happens that some of the car- bonates held in solution by an excess of carbonic acid become insoluble, and are deposited after the escape of that excess. This is the principal cause of the deposits which form in the basins and conducting-pipes of many mineral waters. These deposits vary greatly in composition ; sometimes they are floc- culent or pulverulent, and collect in the form of mud ; some- times they form hard concretions or scales. Calcium and magnesium carbonates, ferric hydrate, alumina, and silica are the most ordinary constituents of such deposits. Besides these, arsenic, various metallic oxides, and materials which it would be difficult to detect in the water itself, are sometimes concen- trated, as it were, in these deposits. Thus, arsenic is detected WATER. 83 much more readily in the ochrey deposits around a ferruginous spring than in the water of the spring itself. ACIDULOUS OR GASEOUS WATERS. Free carbonic acid is the characteristic and predominant element of these waters ; it is dissolved in the depths of the earth under a pressure much greater than that of the atmosphere ; hence a certain portion of the gas is disengaged as soon as the water emerges from the soil, giving rise to a greater or less effervescence. Gaseous waters are cold ; their taste is piquant at the moment of emer- gence, but often becomes saline or even alkaline after the dis- engagement of the greater part of the carbonic acid gas. Nat- ural gaseous waters never consist of a solution of carbonic acid in pure water ; they always contain a small quantity of saline matters, principally traces of sodic, calcic, and magnesic carbonates, and even traces of chlorides and sulphates. Such is the composition of the celebrated Seltzer water and of Soultz- matt water. The water of certain of the Saratoga springs approximates in composition to Seltzer water. ALKALINE WATERS. These waters possess an alkaline re- action, either immediately on their emergence or after the loss of their free carbonic acid. This reaction may be due to an alkaline silicate, but is generally referable to an alkaline car- bonate. Sodium acid carbonate, NaHCO 3 , commonly called bicarbonate of soda, exists in nearly all waters of this class, together with an excess of carbonic acid. Vichy water con- tains about 5 grammes of this salt per litre. CHALYBEATE WATERS. Nearly all waters contain traces of iron in solution ; chalybeate waters are such as contain sufficient of that metal to give them an astringent taste and special therapeutic properties. The iron may exist in three conditions : 1. As ferrous carbonate held in solution by carbonic acid. 2. As ferrous crenate. Berzelius gave the names crenic and apocrenic acids to two bodies which are related to peculiar acids existing in the soil or humus, and which are known as ulmic, humic, and geic acids. Ferrous crenate is soluble in water ; its constitution is not known. 3. As ferrous sulphate. Consequently, chalybeate waters may be carbonated, cre- nated, and sulphated. The ferrous salts are never contained in these waters in large proportions. Many ferruginous waters of undoubted efficacy 84 ELEMENTS OF MODERN CHEMISTRY. do not contain more than 4 or 5 centigrammes per litre. When exposed to the air they lose the greater part of their carbonic acid, and ferrous carbonate is deposited, but this loses its carbonic acid and is converted into brown ferric hydrate. Such is the manner of formation and the nature of the ochrey deposits always noticeable around ferruginous springs. Chalybeate waters are widely diffused. Those of Spa and Pyrmont, Belgium (carbonated), Bussang in the Yosges, and Forges (crenated), and Passy, at Paris, are well known. Cele- brated springs of this class exist at Bedford, Pennsylvania ; others are widely diffused throughout the United States. SALINE WATERS. This class includes a great number of waters charged with various neutral salts, among which are the chlorides, bromides, and iodides. The salts of sodium, mag- nesium, and calcium are those more usually met with in these waters. According to the predominating or peculiarly active principle present, they are classified as chlorinated, sulphated, and bromo-iodated waters. The Saratoga springs yield an acidulo-saline water. Chlorinated Saline Waters. The chlorides generally found in mineral waters are those of sodium, magnesium, and cal- cium ; the former is much the more abundant, and constitutes one of the most common constituents of mineral waters. It communicates to them a pure salty taste, free from bitterness. A great number of saline springs serve for the extraction of sodium chloride. After the evaporation of the water and the deposition of the salt, a mother-liquor remains in which various less abundant salts are concentrated, principally the alkaline bromides and iodides. Sea-water is a chlorinated water. It is well known that it contains a notable proportion of sodium chloride (2.5 to 2.7 per cent.). The common salt is accompanied by the chlorides of magnesium and potassium, and by a considerable quantity of magnesium sulphate (0.6 to 0.7 per cent.). The Dead Sea and the Great Salt Lake of Utah are the most concentrated saline sources known. The water of the latter contains 20 per cent, of sodium chloride. Sulphated Saline Waters. These are characterized by so- dium, magnesium, or calcium sulphate. The springs of Carls- bad, in Bohemia, contain a large proportion of sodium sulphate, together with sodium bicarbonate and sodium chloride. The purgative waters of Epsom, England, contain magne- HYDROGEN DIOXIDE. 85 slum sulphate. The waters of Sedlitz, Saidschiitz, and Pullna, in Bohemia, contain magnesium sulphate and sodium sulphate. Their taste is bitter. The Avon Spring, New York, is of this class. Bromo-iodated Waters. Many mineral waters contain small quantities of bromides and iodides, independently of the chlo- rides which generally exist in much larger proportions. The water of the Dead Sea, so rich in magnesium and sodium chlorides, contain 0.43 per cent, of magnesium bromide. The Iodine Spring at Saratoga contains a notable proportion of alkaline iodides. SULPHUR WATERS. By this name are designated those waters containing a soluble sulphide or sulphuretted hydro- gen. They are either natural sulphur waters or accidental sulphur waters. The first contain sodium sulphide ; they are generally warm, and contain but little solid matter. They all disengage nitrogen on their emergence from the soil. They contain a nitrogenized organic matter (baregine), and some- times deposit a gelatinous precipitate (glairine). Celebrated springs exist in the Pyrenees and at Bagneres- de-Luchon. The sulphur springs of Sharon and Avon, in New York, and the Red and White Sulphur Springs of Virginia are well known. Accidental sulphur waters are those which are formed upon the spot by the reduction of sulphates, and particularly calcium sulphate, contained in the waters. This reduction is accom- plished by the action of organic matters which impregnate the soil, and of which the combustible elements, carbon and hydro- gen, remove the oxygen of the sulphates. It is thus that the sulphur water of Enghien is formed at the gates of Paris. HYDROGEN DIOXIDE. H 2 O 2 This remarkable compound was discovered by Thenard in 1818. It is formed by the action of barium dioxide upon di- lute hydrochloric acid. Barium dioxide, powdered and made into a fine paste with water, is introduced by small portions into cold and dilute hydrochloric acid. It dissolves without disengagement of gas, yielding barium chloride and hydrogen dioxide. BaO 2 4- 2HC1 = Bad 2 + H 2 2 Barium dioxide. Hydrochloric acid. Barium chloride. Hydrogen dioxide. 8 86 ELEMENTS OF MODERN CHEMISTRY. The barium chloride is converted into sulphate, which pre- cipitates, by the cautious addition of dilute sulphuric acid, and at the same time hydrochloric acid is regenerated, so that an additional quantity of barium dioxide may be added, and the operation is several times repeated. Bad 2 + H 2 S0 4 = BaSO + 2HC1 Sulphuric acid. Barium sulphate. The barium chloride finally remaining in solution is exactly precipitated by a solution of silver sulphate, and the hydrogen dioxide poured off and evaporated in vacuo. Pure hydrogen dioxide is a syrupy, colorless, odorless liquid, having a density of 1.452. It is very unstable, and readily gives up half of its oxygen, being converted into water. This decomposition takes place with a brisk effervescence when the dioxide is heated towards 100 ; it is also produced by con- tact with a great number of bodies, some of which are them- selves unaltered, some oxidized, and others even reduced. Hence hydrogen dioxide enters into three classes of reactions. 1. If hydrogen dioxide, or more simply, water charged with hydrogen dioxide, be poured into a test-tube containing man- ganese dioxide, the hydrogen dioxide is instantly reduced with effervescence into water and oxygen. The manganese dioxide remains unchanged. Finely divided platinum, gold, silver, and carbon act in the same manner. 2. Hydrogen dioxide energetically oxidizes arsenic and sele- nium into arsenic and selenic acids. It converts lead sulphide into sulphate. PbS -f 4H 2 2 = PbSO + 4H 2 Lead sulphide. Lead sulphate. 3. Potassium permanganate, KMnO*, is a salt very rich in oxygen ; it dissolves in water, forming a solution having an intense purple color. If hydrogen dioxide be added to it, it is immediately reduced and decolorized. The oxygen from the decomposition of the hydrogen dioxide is in this case added to that from the reduction of the permanganate, and both are dis- engaged in the free state. If hydrogen dioxide be added to a solution of potassium di- chromate, the latter assumes a deep blue color, but this rapidly disappears, giving place to a green tint. At the same time an evolution of oxygen takes place. In this case the reaction is complex : a portion of the hydrogen dioxide oxidizes the HYDROGEN DIOXIDE. 87 chromic acid for an instant into blue perchromic acid, but the latter is instantly reduced, with disengagement of oxygen, by another portion of the hydrogen dioxide, which at the same time loses half of its oxygen. The oxygen gas liberated comes then at the same time from the perchromic acid and the hydrogen dioxide, both of which are supersaturated with oxygen, and which mutually reduce each other. The perchromic acid formed may be removed from the action of the excess of hydrogen dioxide by imme- diately agitating the liquid with ether : the latter dissolves the acid and assumes a dark-blue color. These experiments of reduction are of great interest, and permit of but one explanation. The fact of the reciprocal reduction of two bodies each supersaturated with oxygen can only be explained by admitting that the oxygen of one body possesses an affinity for that of the other, and that the oxygen which is set free is formed by the union of two atoms, one from the hydrogen dioxide, the other from the perchromic or per- manganic acid. These two atoms unite to form a molecule of oxygen OO. This would represent oxygen in the free state, and occupy two volumes. It would be a true combination, and we here encounter for the first time the important notion that the atoms of certain elements are not isolated when in the free state, but combined in pairs, each pair being held together by chemical force. Free oxygen would then be oxygen oxide, a combination of two atoms of oxygen, both together forming a molecule, and occupying two volumes like the molecule of water. 1 molecule of water .... H-O-H = 2 volumes. 1 molecule of oxygen . . . 0=0 = 2 volumes. While the molecular structure of free oxygen or oxygen oxide corresponds in a measure to that of hydrogen oxide or water, there exists a peroxide of oxygen which corresponds in a measure to hydrogen peroxide ; it is ozone. Hydrogen dioxide H-O-O-H Oxygen dioxide (ozone) 0\ I X 88 ELEMENTS OF MODERN CHEMISTRY. SULPHUR Vapor density compared to air 2.22 Vapor density compared to hydrogen .... 32. Atomic weight S =32. Sulphur has been known from the greatest antiquity. In certain volcanic countries it is found on the surface of the earth in the native state. Sicily and Iceland contain large deposits in the neighborhood of extinct volcanoes (solfatares). In order to separate it from the earthy matters which accompany it, it is subjected in Sicily to distillation in earthen pots (Fig. 32). FIG. 32. These are arranged in two rows in furnaces, and communicate by lateral tubulures with other pots which are placed outside of the furnace, and in which the sulphur vapor is condensed. Crude sulphur is thus obtained ; it is still mixed with foreign matters, from which it is separated by a new distillation. This operation, which is called refining, is conducted in an apparatus represented in Fig. 33. A horizontal cast-iron cylinder, A, receives the melted sul- phur from the vessel C, which is heated by the waste gases from the furnace, and which serves as a reservoir. The sulphur vapor enters a large masonry chamber, B, the floor of which is SULPHUR. 89 slightly inclined in order that the condensed liquid sulphur may flow towards a tap, H, which can be opened as is necessary. A damper, R, that can be regulated by an articulated wire, per- mits the closing and opening of the mouth of the cylinder. The vault of the chamber is provided with a safety-valve, K, which allows of the escape of the expanded air. At the commencement of the operation, when the walls of the chamber are cold, the sulphur condenses in the form of a fine powder, which is known as flowers of sulphur. But when the walls of the chamber become heated above the melting- point of sulphur, the vapor condenses into a liquid, and on opening the tap at H, it is drawn off into a vessel, E, from which it is distributed into slightly conical or cylindrical moulds, where it solidifies. Roll sulphur is thus obtained. FIG. 33. Physical Properties. Sulphur is a lemon-yellow solid. It is tasteless, odorless, and brittle ; it is a non-conductor of heat and electricity. A stick of sulphur pressed in the hand or plunged into warm water produces a crackling sound, and finally breaks into pieces ; this is due to the unequal expan- sion from the circumference to the centre of the non-conduct- 8* 90 ELEMENTS OF MODERN CHEMISTRY. ing mass of sulphur, the crystalline particles of which are but slightly held together by cohesion. The density of sulphur is about 2.03. At 111.5 it melts into a brownish-yellow, transparent liquid. If this liquid be allowed to cool slowly until a crust forms upon the surface, and the crust be pierced and the part still remaining liquid be decanted, after removing the crust the interior of the vessel is found covered with long, transparent, flexible needles of a brownish-yellow color. These crystals are oblique-rhombic prisms having a density of 1.98. This is not the only crystal- line form assumed by sulphur. If a solution of sulphur in carbon disulphide be allowed to evaporate spontaneously, right-rhombic octahedral crystals are deposited having a den- sity of 2.05. This form is also that of native crystallized sulphur. Sulphur crystallizes, then, in two distinct forms belonging to two distinct crystalline systems. It is dimorphous. It is a curious fact that the prisms formed by way of fusion do not long retain their transparence and their flexibility. When aban- doned for some time to ordinary temperatures, they become opaque and brittle. They are then found to be traversed by a multitude of planes of cleavage, which are the faces of microscopic octahedra similar to those obtained by way of solution. Reciprocally, the transparent octahedral crystals become opaque when maintained for some time at a temperature of 111; they are then transformed into a multitude of little crystals of prismatic sulphur. It is seen that the two crystal- line modifications of sulphur can be transformed into each other. It is a curious instance of dimorphism. Sulphur melted in a sealed tube will remain liquid for a long time at temperatures below its ordinary point of solidifi- cation ; it is then said to be in a state of superfusion. When it finally solidifies, it crystallizes in voluminous octahedra having the form of crystallized native sulphur (Schiitzen- berger). There are other and amorphous modifications of sulphur. Experiment. If sulphur be melted in a flask, and the tem- perature be gradually raised above its point of fusion, it as- sumes a thick consistence and a dark color. At 220 it has a brown-red color and is very thick. If while in this state it be poured into cold water, it is converted into a soft, transparent, SULPHUR. 91 brownish-yellow, and elastic mass. It has lost all crystalline appearance ; it has become amorphous, and is now soft sulphur. When abandoned to itself for several days, it hardens, becomes opaque, and reassumes the properties of ordinary sulphur. This change takes place immediately if the soft sulphur be heated to 90 or 95 ; is then accompanied by a sensible disen- gagement of heat (Regnault). There are two modifications of soft sulphur. If it be treated with carbon disulphide, a part of it is dissolved, and a residue remains. The soluble part constitutes soluble soft sulphur; the residue is insoluble soft sulphur (Ch. Sainte-Claire Deville). In recently-sublimed flowers of sulphur the sulphur exists in the amorphous condition. Sulphur boils at 440 ; its vapor is red. At 500 it has a density of 6.654 (Dumas). Towards 1000 its density is only about one-third as great. According to H. Deville and Troost, the vapor density of sulphur, determined at 860 and reduced by calculation to 0, is 2.22. Compared to hydrogen, this density is equal to 32, which is the normal density of sulphur vapor, and gives its atomic weight. If 1 volume of hydrogen weighs 1, 1 volume of sulphur vapor weighs 32 ; the latter figure is therefore the atomic weight of sulphur. But at a temperature a little above its point of ebullition the vapor density of sulphur is 6.6, or three times greater than at 860 ; this is accounted for by the fact that the sulphur does not assume the true gaseous state below a temperature of 860. Sulphur is insoluble in water, but very slightly soluble in alcohol, a little more soluble in ether and benzine. Its best solvent is carbon disulphide. Chemical Properties. Sulphur possesses energetic affini- ties. It combines directly with a great number of the other elements. It is well known that it is combustible, burning with a blue flame. Its combustion in air or oxygen produces sulphurous oxide. Sulphur combines directly with chlorine, bromine, iodine, phosphorus, arsenic, and carbon, and with very many of the metals. Iron and copper burn in the vapor of sulphur. The sulphides thus formed generally possess the atomic constitution of the corresponding oxides. Thus, the compound of sulphur and carbon, carbon disulphide, is analogous to carbonic acid gas. This analogy is maintained between a great number of 92 ELEMENTS OF MODERN CHEMISTRY. oxygen and sulphur compounds, as will be seen by the follow- ing examples : H 2 water. H 2 S hydrogen sulphide. KOH potassium hydrate. KSH potassium sulphydrate. CO 2 carbon dioxide. CS 2 carbon disulphide. K 2 potassium monoxide. K 2 S potassium monosulphide. BaO barium monoxide. BaS barium monosulphide. K 2 C0 3 potassium carbonate. K 2 CS 3 potassium sulphocarbonate. SULPHYDRIC ACID, OR HYDROGEN SULPHIDE. Density compared to air 1.192 Density compared to hydrogen 17. Molecular weight H 2 S =34. This gas, known also as sulphuretted hydrogen, was discov- ered by Meyer and Rouelle, and studied by Scheele, in 1777, and by Berthollet. Preparation. Hydrogen sulphide may be prepared by FIG. 34. gently heating antimony trisulphide in a flask with hydrochlo- ric acid (Fig. 34). The gas is first passed through a wash- HYDROGEN SULPHIDE. 93 bottle, B, containing a little water, and may then be collected over the pneumatic trough. The reaction which takes place is expressed by the following equation : Sb 2 S 3 -f 6HC1 2SbCP + 3H 2 S Antimony trisulphjde. Hydrochloric acid. Antimony trichloride. The gas is generally prepared in the laboratory by the reaction of dilute sulphuric acid with ferrous sulphide. The operation requires no heat, and the reaction is as follows : FeS + H 2 SO* == FeSO + H 2 S Ferrous sulphide. Sulphuric acid. Ferrous sulphate. As hydrogen sulphide is largely used in the laboratory, the apparatus represented in Fig. 35 is convenient for its ready production. It is composed of two large bottles, of which the FIG. 35. lower apertures are connected by a large caoutchouc tube. In one of these bottles is placed a layer of broken glass or coke, which is not attacked by sulphuric acid ; upon this is placed the ferrous sulphide in fragments. The neck of this bottle is closed by a cork, through which passes a glass tube bearing a stop-cock. The second bottle is nearly filled with dilute sul- phuric acid. The stop-cock of the first bottle being opened, the sulphuric acid enters until it attains the same level in both bottles, and as soon as it reaches the ferrous sulphide the reac- tion commences and hydrogen sulphide is disengaged. If the 94 ELEMENTS OF MODERN CHEMISTRY. stop-cock be closed, the continued evolution of gas drives the liquid back into the second bottle, until the disengagement of gas ceases, which takes place as soon as the sulphuric acid no longer touches the ferrous sulphide. The first bottle then serves as a reservoir of hydrogen sulphide, containing the gas under a pressure greater than that of the atmosphere, and which can be increased by elevating the second bottle. In order to obtain a current of the gas, it is sufficient to open the stop-cock, and the flow can be regulated at will. Physical Properties. Hydrogen sulphide is a colorless gas. It has a penetrating odor of putrid eggs. Under a pressure of 17 atmospheres, it condenses to a transparent, strongly refract- ing liquid, having a density of about 0.91. At 85.5 this liquid solidifies to a white crystalline mass (Faraday). Hydro- gen sulphide is soluble in water. At 0, one volume of water dissolves 4.37 volumes ; at 10, 3.58 volumes ; and at 20, 2.90 volumes. Composition. 2 volumes of hydrogen sulphide contain 2 volumes of hydrogen and 1 volume of sulphur vapor. If a given volume of this gas be introduced into a bent tube over mercury (Fig. 22), and a morsel of tin be then introduced and heated for about twenty minutes, the hydrogen sulphide is decomposed ; the sulphur combines with the tin, and the hy- drogen is set free. After cooling, the latter gas occupies a volume exactly equal to that of the hydrogen sulphide at first contained. If, then, from the vapor density of hydrogen sulphi'de == 17 we subtract the density of hydrogen = 1 we find the number 16 which represents half the density of sulphur vapor. It is hence concluded that one volume of hydrogen sulphido contains half a volume of sulphur vapor to one volume of hy- drogen. It is also seen that hydrogen sulphide has exactly the same chemical constitution as vapor of water. H 2 O = 2 volumes or one molecule of vapor of water. H 2 S ^= 2 volumes or one molecule of hydrogen sulphide. The analogy between sulphur and oxygen is here manifested in a striking manner. One atom of each of these elements requires two atoms of hydrogen. This is. expressed by saying that both oxygen and sulphur are diatomic elements. HYDROGEN SULPHIDE. 95 Chemical Properties. Hydrogen sulphide is combustible, burning with a bluish flame. The products of its complete combustion are water and sulphurous oxide. When mixed with one and a half times its volume of oxygen, it explodes on the application of a flame or the passage of an electric spark. H 2 S -f- O 3 = SO 2 + H 2 Two volumes. Three volumes. Two volumes. Two volumes. When the supply of oxygen is insufficient, the combustion is incomplete and sulphur is deposited. In the presence of water, this oxidation takes place at ordi- nary temperatures, occasioning a deposit of sulphur. In the presence of moisture and porous matters it goes further, sul- phuric acid being formed. Hydrogen sulphide has a feeble acid reaction ; it changes blue litmus to a wine-red color. When it reacts with potassium hydrate, water and potassium sulphydrate are formed. H} S + Hydrogen sulphide. Potassium hydrate. Potassium sulphydrate. Chlorine, bromine, and iodine decompose hydrogen sulphide, combining with its hydrogen. When these bodies are dry, the action is energetic, and the sulphur combines with the excess of the element employed. If water be present, the sulphur is set at liberty. Bodies rich in oxygen readily decompose hydrogen sulphide. Experiments. 1. If a few drops of the strongest nitric acid be poured into a jar filled with hydrogen sulphide, the gas is instantly inflamed. The nitric acid gives up oxygen, water is formed, sulphur is set free, and abundant red fumes appear at the same time. 2. If four volumes of hydrogen sulphide be mixed with two volumes of sulphurous oxide over the mercury-trough, a deposit of sulphur is at once formed. 2H 2 S + SO 2 = 2H 2 + 3S Hydrogen sulphide. Sulphurous oxide. Water. Sulphur. (4 volumes.) (2 volumes.) Hydrogen sulphide decomposes a great number of metallic solutions, forming insoluble sulphides, which are precipitated. Experiments. 1. If a solution of hydrogen sulphide be added to a solution of blue vitriol or cupric sulphate, a brown 96 ELEMENTS OF MODERN CHEMISTRY. precipitate of cupric sulphide is formed. The reaction is expressed by the following equation : CuSO -f IPS = CuS + H'SO* Cupric sulphate. Cupric sulphide. Sulphuric acid. 2. By an analogous reaction, a solution of plumbic acetate, or a paper impregnated with that salt, is at once blackened by the presence of hydrogen sulphide. Hydrogen sulphide acts as a poison if inhaled in large quantities or for any length of time. HYDROGEN PERSULPHIDE. This compound, discovered by Thenard, is analogous to hy- drogen dioxide. It is prepared by pouring, drop by drop, a solution of calcium disulphide into dilute hydrochloric acid. CaS 2 + 2HC1 = CaCP + H 2 S 2 Calcium disnlphide. Hydrochloric acid. Calcium chloride. Hydrogen disulphide. Hydrogen disulphide is formed and collects at the bottom of the vessel in the form of a yellowish oil, having a disa- greeable, irritating odor. Towards 60 or 70 it decomposes rapidly into hydrogen sulphide and sulphur. H 2 S* = H 2 S + S This decomposition takes place slowly at ordinary tempera- tures. Hofmann attributes to this body the formula H 2 S 3 . He has obtained a compound of this sulphide with an alkaloid, strych- nine, the analysis of which has led him to conclude that there are three atoms of sulphur in a molecule of the persulphide of hydrogen. OXYGEN ACIDS OF SULPHUR. 1. Sulphur forms three compounds with oxygen : ( sulphurous anhydride or Sulphurous oxide SO 2 - ,, A sulphur dioxide, ilphuric anhydri sulphur trioxide. T, 11- -j 02/-17 (recently discovered by Persulphunc oxide S'O 7 j Beri f helot a , , . . , ar\s ( sulphuric anhydride or Sulphuric oxide sulphur trioxide. SULPHUROUS OXIDE. 97 2. By combining with a molecule of water, these oxides are converted into the corresponding acids. 50 2 + H'O = H 2 S0 3 sulphurous acid. 50 3 + H 2 = H 2 S0 4 sulphuric acid. 3. There are two other important acids of sulphur, hypo- sulphurous and hyposulphuric acids. The former may be con- sidered as sulpho-sulphuric acid, that is, sulphuric acid in which 1 atom of oxygen is replaced by an atom of sulphur. H 2 S0 4 sulphuric acid. H 2 (S0 3 )S sulpho-sulphuric or hyposulphurous acid. Hyposulphuric acid may be considered as resulting from the addition of sulphurous oxide to sulphuric acid. SO 2 + H 2 S0 4 == H 2 S 2 6 hyposulphuric acid. 4. These are not the only known sulphur acids. Hyposulphuric acid, which is called also dithionic acid, is the first of a series of acids, each of which contains 2 atoms of hydrogen and 6 atoms of oxygen, the number of sulphur atoms regularly increasing. This series is called the thionic series. The following is the nomenclature and composition of the acids : H 2 S 2 6 dithionic, hyposulphuric acid. H 2 S 3 6 trithionic acid. H 2 S 4 6 tetrathionic acid. H 2 S 5 6 pentathionic acid. 5. Schiitzenberger has recently made known a new sulphur acid, which he has named hydrosulphurous acid, and which is formed by the action of zinc upon sulphurous acid, as will be described farther on. The composition of this acid is repre- sented by the formula H 2 S0 2 . There is an interesting relation between this acid and sul- phurous and sulphuric acids. H 2 S0 2 hydrosulphurous acid. H 2 S0 3 sulphurous acid (not yet isolated). H 2 SO* sulphuric acid. SULPHUROUS OXIDE. Density compared to air 2.234 Density compared to hydrogen 32. Molecular weight SO 2 =64. E 9 98 ELEMENTS OF MODERN CHEMISTRY. Sulphurous oxide or sulphurous acid gas may be prepared by decomposing sulphuric acid with copper. The metal in small clippings and the acid aro introduced into a flask fitted FIG. 36. with a delivery-tube (Fig. 36) ; heat is applied and the gas collected over the mercury-trough. The reaction which takes place is expressed by the following equation : Cu + 2H 2 SO* = CuSO 4 -f 2H 2 + SO 2 Copper. Sulphuric acid. Cupric sulphate. A solution of sulphurous acid in water is often needed in the laboratory. It may be conveniently prepared by reducing sulphuric acid by charcoal ; the products of the reaction are water, and sulphurous and carbonic acid gases. 2H 2 SO* + C = 2H 2 4- 2S0 2 -f CO 2 Sulphuric aciil. Carbon dioxide. The mixed gas is passed through a series of bottles contain- ing water, which dissolves the sulphurous oxide, but takes up only an insignificant quantity of the carbon dioxide. Physical Properties. Sulphur dioxide is a colorless gas having a pungent, suffocating odor. It is readily liquefied by being led into a vessel surrounded by a mixture of ice and salt. It condenses at ordinary temperatures, under a pressure of about two atmospheres. The liquid has a density of 1.45 ; it boils at 10, and produces great cold by its evaporation ; on this account it is used for the manufacture of ice, and in other cases where intense cold is required. 73 may be obtained SULPHUROUS OXIDE. 99 by the evaporation of liquid sulphurous acid aided by double- acting pumps (Raoul Pictet). Water at dissolves 79.9 times its volume of sulphurous oxide, and only 39.4 volumes at 20. Experiments. 1. If a small quantity of mercury contained in a porcelain capsule be covered with a deep layer of liquid sulphurous oxide, and the evaporation of the latter be favored by directing a rapid current of air over its surface, the mercury is frozen into a solid button. 2. When liquid sulphurous acid is poured into not too great a quantity of water, a part of it is dissolved, but the excess absorbs heat from the mass of liquid, volatilizes suddenly, and the water is frozen. Chemical Properties. Sulphurous oxide is not decom- posed by heat. It is incombustible, and extinguishes burning bodies. Its most striking property is its affinity for oxygen. If a mixture of two volumes of sulphurous oxide and one volume of oxygen be passed through a tube containing slightly heated spongy platinum, the two gases combine, forming sulphuric oxide (Kuhlmann). A solution of sulphurous oxide in water slowly absorbs oxy- gen, and is converted into sulphuric acid. It may be admitted that the aqueous solution contains the veritable sulphurous acid. H 2 S0 3 + O = H 2 SO Sulphurous acid. Sulphuric acid. Sulphurous acid reduces a great number of oxidized bodies. At ordinary temperatures it takes the oxygen from iodic acid, setting free the iodine ; but the latter disappears on the addi- tion of an excess of sulphurous acid, sulphuric and hydriodic acids being formed. H 2 S0 3 -j- H 2 + P = H 2 SO -f 2HI It decolorizes the purple solution of potassium permanganate, forming manganese sulphate and potassium sulphate. It con- verts arsenic acid into arsenious acid. It combines directly with lead dioxide, forming lead sulphate. PbO 2 + SO 2 = PbSO 4 Lead dioxide. Lead sulphate. Chlorine will unite directly with sulphurous oxide. If a mixture of equal volumes of chlorine and sulphurous oxide be 100 ELEMENTS OF MODERN CHEMISTRY. exposed to sunlight, the two gases combine, forming a liquid having a suffocating odor. It is sulphuryl chloride. Its den- sity is 1.66, and its boiling-point is 77. It may be regarded as sulphur trioxide in which one atom of oxygen is replaced by two atoms of chlorine. SO 3 = (SO 2 )"0 sulphuryl oxide or sulphuric oxide. S0 2 CP = (S0 2 /'C1 2 sulphuryl chloride. In these reactions in which the sulphurous oxide combines directly with either one atom of oxygen or two atoms of chlorine, it plays the part of an element ; it is a compound radical, and this radical is diatomic, because it unites with two atoms of the monatomic element chlorine, or with one atom of the diatomic element oxygen, which is equivalent to two atoms of chlorine. In the formulae given, the diatomicity is expressed by the accents ". Sulphurous acid bleaches various vegetable and animal mat- ters. A bouquet of violets or a rose is bleached in a few minutes by a solution of sulphurous oxide. Sulphurous oxide is employed in the arts to bleach wool. HYDRO-SULPHUROUS ACID. H 2 SO 2 While sulphurous acid reduces a number of bodies, it is in its turn reduced by the action of zinc upon its aqueous solution. A yellow liquid is thus obtained which energetically bleaches indigo and litmus solutions (Schbnbein). Schiitzenberger has shown that the liquid gifted with these properties contains the zinc salt of a new acid, which he has named hydrosulphurous. This acid is formed by the combination of hydrogen with sul- phurous oxide. The reaction is expressed by the following equations : H 2 S0 3 + Zn = ZnSO 3 + H 2 Sulphurous acid. Zinc. Zinc sulphite. SO 2 + H 2 ' = H 2 S0 2 Sulphurous oxide. Hydrosulphurous acid. When this liquid is treated with very dilute sulphuric acid, it gives a liquor of a dark orange-yellow color, having ener- getic bleaching powers. It then contains hydrosulphurous acid. It soon becomes clouded and deposits sulphur. This SULPHUR TRIOXIDE, OR SULPHUH'C OXIOE. 101 acid is not stable, but its acid sodium salt is more so ; the latter has the composition NaHSO 2 . It readily absorbs oxygen from the air, being converted into sodium acid sulphite. NaHSO 2 + O = NaHSO 3 This oxidation is also brought about by the presence of cer- tain metallic salts, such as those of copper, mercury, and lead. In this case the metal is reduced and precipitated, and the hydrosulphite is decomposed, yielding sulphurous oxide. NaHSO 2 -f CuSO 4 === NaHSO* -f SO 2 + Cu Sodium hydrosulphite. Cupric sulphate. Sodium acid sulphate. Sodium acid hydrosulphite may be obtained by the electro- lysis of a solution of sodium acid sulphite. In this case the hydrogen, which would otherwise be disengaged at the negative pole, accomplishes the reduction. NaHSO 3 + H 2 = NaHSO 2 + H 2 O SULPHUR TRIOXIDE, OR SULPHURIC OXIDE. (SULPHURIC ANHYDRIDE.) Vapor density compared to hydrogen 40. Molecular weight SO 3 =80. Sulphur trioxide is formed by the union of oxygen with sul- phurous oxide in the presence of finely-divided platinum. It is prepared by gently heating fuming sulphuric acid in a retort ; vapors are given off which, when condensed in a re- ceiver surrounded by a freezing mixture, solidify into a white mass, having a fibrous appearance and a silky lustre. Sulphur trioxide boils at a temperature between 30 and 35. At ordinary temperatures it produces white fumes in the air by condensing the atmospheric moisture. Its most striking property is its affinity for water ; when thrown into that liquid, it becomes hydrated with such energy that a portion of the water is suddenly vaporized, and a hissing noise is produced similar to that heard on plunging a red-hot iron into water. Sulphuric acid is formed by the reaction. SO 3 + H 2 = H 2 S0 4 9* HJ2iV ; \ : SLEMSJfT^ OF MODERN CHEMISTRY. SULPHURIC ACID. Molecular weight H 2 S0 4 : This acid, which has been known for centuries, was formerly obtained by the distillation of ferrous sulphate. Large quan- tities of it are now consumed in the arts, and it is manufac- tured in extensive apparatus known as leaden chambers. Sul- phurous oxide is conducted into these chambers, where it meets with nitric acid, by which it is oxidized. SO 2 + 2HN0 3 = H 2 S0 4 + 2N0 2 Nitric acid. Nitrogen peroxide. The products of the first reaction are sulphuric acid and nitrogen peroxide (red vapors) ; but the latter is decomposed by steam, which is injected into the chamber ; nitric acid is regenerated and nitrogen dioxide is formed. 3N0 2 + H 2 == 2HN0 3 + NO Nitrogen peroxide. Nitrogen dioxide. But the nitrogen dioxide is not lost ; it combines with the oxygen of the air contained in the chamber, and is reconverted into nitrogen peroxide. NO -f- = NO 2 The latter is again decomposed into nitric acid and nitrogen dioxide by the action of water, and the sulphurous oxide which continually arrives in the chamber always encounters nitric acid, by which it is converted into sulphuric acid. It is a continuous operation, which theoretically leaves no residue, and permits of the conversion of an indefinite amount of sul- phurous oxide into sulphuric acid. It is really the oxygen of the air, continually absorbed and given up by the nitrogen dioxide, which effects the oxidation of the sulphurous oxide ; the nitric acid is the direct agent, and the nitrogen dioxide is intermediate, for it is the vehicle for the transfer of the oxygen. Fig. 37 represents a section of a series of leaden chambers for the manufacture of sulphuric acid. Sulphur is burned in two furnaces, AA, and the heat gen- erated is employed to boil the water contained in the boilers SULPHURIC ACID. 103 104 ELEMENTS OP MODERN CHEMISTRY. above the flame, the steam being distributed to the chambers by the pipes c d. The sulphurous oxide, together with a great excess of air, passes through the pipes BB into a leaden drum, C. A thin layer of sulphuric acid charged with nitrous products trickles over the inclined shelves in the drum. The gases pass first into the chamber C, then into D, where they meet with nitric acid, which falls in thin layers over a double cascade, EE, in such a manner as to present a large surface for the action of the sulphurous oxide. The sulphuric acid which is formed in this chamber is charged with nitrous products ; it is therefore allowed to flow by the inclined tube F into the chamber C, where it encounters an excess of sulphurous oxide, and which is called the denitrifier. The sulphurous oxide, the excess of air, and the nitrogen peroxide pass from D into the large chamber HH, into which steam is projected by several jets. Here the larger portion of the sulphuric acid is pro- duced, and the reaction is completed in another chamber. In the engraving the last two chambers are not fully represented. The gases from the last chamber enter a refrigerator, in which the condensation takes place ; they are lastly conducted into a leaden column, R, filled with coke which is kept saturated with sulphuric acid by a thin stream from the reservoir 0. This acid completely absorbs the nitrogen dioxide, and descends by the tube ba into the reservoir t, situated near the furnace. As soon as this reservoir is full, the stop-cock r is closed, and / is opened ; the pressure of the steam then forces the acid up into the reservoir #, which feeds the first drum. The gas which escapes from the last column, which is known as Gay- Lussac's column, consists of nitrogen charged with an insig- nificant quantity of nitrous products. The acid which is drawn from the chambers is not suffi- ciently concentrated, having a density of only about 1.5. It is first evaporated in leaden vessels until it becomes strong enough to act upon the lead, and the concentration is then fin- ished in large platinum retorts. The excess of water is thus driven out. The concentrated acid possesses a density of 1.842. In many manufactories pyrites is burned instead of sulphur. Sulphurous oxide is produced, and a residue of ferric oxide remains. Purification of Sulphuric Acid. The sulphuric acid of commerce contains impurities. It holds in solution a small SULPHURIC ACID. 105 quantity of lead sulphate, formed in the evaporating basins ; it is often charged with nitrous products, and sometimes with ar- senic acid, when the sulphurous oxide employed in its prepa- ration has been obtained by the combustion of arsenical pyrites. It may be freed from these impurities by distillation. The nitrous products are first disengaged, and are found in the first portions of the distillate, which must be rejected. Pure sul- phuric acid then passes ; the lead sulphate and arsenic acid remain in the retort with the last portions of the acid, which must not be distilled. The operation may be conducted in a glass retort connected with a cooled receiver. The retort should be heated laterally by an annular flame so that explosive evolution of vapor may be avoided, and it is well to introduce some platinum wires with the acid, and to cover the retort with a sheet-iron hood. Constitution of Sulphuric Acid. Since oxygen combines directly with sulphurous oxide to form sulphuric oxide, the latter may be regarded as sulphuryl oxide, S0 2 0. Sulphuric acid is the hydrate of this oxide. SO 3 + H 2 = H 2 S0 4 The following experiment indicates the relations which exist between the elements composing this hydrate. If sulphuryl chloride be poured into water, it disappears, sulphuric acid and hydrochloric acid being formed. HOH OH + 2HC1 Sulphuryl 2 molecules Sulphuric 2 molecules chloride. of water. acid. hydrochloric acid. Sulphuric acid is .thus formed by the decomposition of 2 molecules of water, of which 2 atoms of hydrogen have been removed by 2 atoms of chlorine, and replaced by the group SO 2 . It may then be truly said that sulphuric acid is derived from two molecules of water by the substitution of the diatomic radical (SO 2 )" for two monatomic atoms of hydrogen. H.OH , ( OH H.OH 3 ) {OH 2 molecules of water. Sulphuric acid. If the composition of sulphuric acid be compared to that of sulphuryl chloride, from which it may be formed, it will be E* 106 ELEMENTS OF MODERN CHEMISTRY. seen that both compounds contain the same nucleus or radical SO 2 , and that instead of the two atoms of chlorine of the chloride, the acid contains two groups OH. The group OH is a residue, as it were, which represents a molecule of water minus one atom of hydrogen, and which is called hydroxyl. It is a monatomic group, and sulphuric acid is formed by the saturation of the affinity of the diatomic radical sulphuryl by two monatomic groups hydroxyl, which replace the two atoms of chlorine of sulphuryl chloride. Williamson has described an intermediate compound in which the radical sulphuryl is combined with one atom of chlorine and one OH group. ! SO '{OH SO! {OH Sulphuryl chloride. Sulphuryl chlorohydrate. Sulphuric acid. The sulphur in sulphuric acid is hexatomic. O HO-S-OH 6 Physical Properties. Sulphuric acid is a colorless oily liquid ; its density at 12 is 1.842 (Marignac). Its boiling-point is 325, and it solidifies at 34. If it be crystallized several times at a low temperature, and the part remaining liquid be decanted off each time, the melting-point is gradually raised to -[-10.5, where it remains stationary. According to Marignac, the acid which solidifies and fuses at -f-10.5 constitutes the true monohydrated acid, H 2 S0 4 . At a temperature about 40 it emits some fumes, and between this point and 290 it disen- gages a small quantity of vapor of sulphuric oxide. At 290 it begins to boil, but its boiling-point soon rises to 338, where it remains. Such are, according to Marignac, the properties of monohydrated sulphuric acid. According to this chemist, the acid purified by simple distillation, and boiling at 325, still contains a small amount of water. Chemical Properties. When exposed to a red heat, sul- phuric acid decomposes into sulphurous oxide, oxygen and water. H 2 S0 4 = SO 2 -f O + H 2 Many bodies having an affinity for oxygen reduce sulphuric SULPHURIC ACID. 107 acid by the aid of heat. Thus sulphur effects the reduction, being at the same time oxidized to sulphurous oxide. 2H 2 SO -f S = 3S0 2 + 2H 2 O We have already studied the action of charcoal and copper upon sulphuric acid when boiled with that liquid, and we have seen that zinc and iron decompose the dilute acid with evolu- tion of hydrogen and formation of a sulphate. Sulphuric acid has a strong affinity for water. When four parts of sulphuric acid are quickly mixed with one part of water, the temperature rises to above 100. If the experiment be made with large quantities, it is not without danger, and re- quires prudence lest part of the acid be projected from the vessel. Experiments. If four parts of sulphuric acid be quickly added to one part of snow, the latter is immediately liquefied and a notable elevation of temperature takes place ; for the energy of the combination of the sulphuric acid with the water is so great that the heat produced by the union is greater than that consumed in the liquefaction of the ice. But if four parts of snow be mixed with one part of sul- phuric acid, the result is the reverse ; there is a lowering of temperature. The affinity of sulphuric acid for water is manifested in a number of reactions. In the following it is sufficiently power- ful to cause the formation of the water it requires : If a morsel of sugar be moistened with sulphuric acid, it becomes blackened and carbonized in a few minutes. The sugar contains no water already formed, but independently of carbon it contains hydrogen and oxygen in the proportions necessary to form water, so that the latter compound is produced by the influence of the sulphuric acid, and a carbonaceous matter remains. This water which is absorbed by sulphuric acid with so much energy, combines with the acid in a manner analogous to that in which water of crystallization combines with certain salts. Indeed, if sulphuric acid to which 18.3 per cent, of water has been added be exposed to a temperature of 0, large prismatic crystals are formed, which remain solid even at a temperature of -f-*7 or -}-8 . The composition of these crystals is ex- pressed by the formula H 2 SO*,H 2 0. They constitute a dihy- drated acid, for they result from the union of two molecules of water with one molecule of sulphuric oxide. 108 ELEMENTS OF MODERN CHEMISTRY. Sulphuric acid is a dibasic acid ; that is, it contains two atoms of hydrogen that are replaceable by an equivalent quantity of metal. This substitution takes place when the acid is treated with a hydrate, such as potassium hydrate, or with an oxide, such as lead oxide. H 2 SO -f- 2KOH == K 2 S0 4 -f 2H 2 O Potassium hydrate. Potassium sulphate. H 2 S0 4 -f PbO === PbSO 4 -f H 2 Lead oxide. Lead sulphate. When saturated with potassium hydrate, the sulphuric acid is converted into potassium sulphate, and, in the salt, two atoms of potassium replace the two atoms of hydrogen of the acid. In the case of the lead oxide, on the contrary, the reaction, which is only a double decomposition, takes place so that a single atom of lead replaces the two atoms of hydrogen. The metal lead is then said to be diatomic ; that is, one atom of lead is capable of replacing two atoms of a monatomic element such as hydrogen, and one atom of lead is equivalent to two atoms of potassium. Sulphuric acid may be detected by the following reactions, which are also applicable to the soluble sulphates. In solutions containing sulphuric acid or a sulphate, barium salts produce a white pulverulent precipitate, which is insolu- ble in either cold or hot nitric acid ; this precipitate is barium sulphate. When mixed with an excess of charcoal and heated to whiteness, it is converted into barium sulphide. BaSO + 4C = 4CO ' BaS Barium sulphate. Carbon monoxide. Barium sulphide. The sulphide of barium disengages hydrogen sulphide when it is moistened with hydrochloric acid ; this gas may be recog- nized by its odor and by its blackening a paper impregnated with lead acetate. FUMING SULPHURIC ACID. Fuming sulphuric acid, or Nordhausen sulphuric acid, as it was formerly called, can be regarded as a combination of sul- phuric acid and sulphuric oxide. SO'< H H 2 S0 4 -f SO 3 = H 2 S 2 7 = O S0 2 < OH HYPOSULPHUROTJS ACID. 109 It is a light-brown, oily liquid. At it solidifies into a leafy mass. It gives off white fumes in the air. When heated, it decomposes into sulphuric oxide and sulphuric acid. It is ob- tained in the arts by the distillation of ferrous sulphate that has been previously transformed into ferric subsulphate by roasting. This subsulphate is calcined in stoneware retorts ; it gives off sulphuric oxide when it is perfectly dry, but as it is difficult to entirely free it from water of crystallization, the vapor of sulphuric oxide is mixed with that of sulphuric acid, and the mixed vapors are condensed in cooled receivers. The residue of the distillation is ferric oxide, Fe 2 3 . HYPOSULPHUROUS OR SULPHO-SULPHURIC ACID. This acid is not known in the free state. When sodium hyposulphite is treated with dilute sulphuric acid, the hypo- sulphurous acid set free is at once decomposed into sulphurous acid and sulphur. Na 2 S 2 3 -f H 2 SO* == Na 2 SO + H 2 S0 3 + S Sodium hyposulphite. Sodium sulphate. Sodium hyposulphite is formed when sulphur is boiled with a solution of sodium sulphite. Na 2 S0 3 -f S = Na 2 S(S0 3 ) Sodium sulphite. Sodium hyposulphite. It is a very soluble salt, forming voluminous crystals. HYPOSULPHURIC ACID. If fuming sulphuric acid represent a combination of sul- phuric acid and sulphuric oxide, hyposulphuric acid can be regarded as resulting from the union of sulphuric acid with sulphurous oxide. S0 3 .H 2 SO* fuming sulphuric acid. S0 2 .H 2 SO hyposulphuric acid. Preparation. Hyposulphuric acid is prepared by passing sulphurous oxide into water in which manganese dioxide is sus- pended. 2S0 2 + MnO 2 = MnS 2 6 Manganese dioxide. Manganese hyposulphate. 10 110 ELEMENTS OF MODERN CHEMISTRY. Manganese hyposulphate is thus formed, and this is con- verted into barium hyposulphate by a double decomposition with barium sulphide. The liquid is separated from the man- ganese sulphide by filtration, and exactly decomposed with dilute sulphuric acid. Barium sulphate is precipitated, and the hyposulphuric acid remains in solution. The liquid is then concentrated in vacuo. Properties. Hyposulphuric acid is a very acid, syrupy liquid, having a density of 1.347. It is not stable ; when boiled it decomposes into sulphuric acid and sulphurous oxide. PERSULPHURIC OXIDE. This body has been very recently discovered by Berthelot, who obtained it in the pure state by the action of silent elec- tric discharges of high tension upon a mixture of equal vol- umes of sulphurous oxide and oxygen, both perfectly dry. Persulphuric oxide is formed, and there remains a residue of oxygen. S 2 4 -f O 4 S 2 7 -f 4 vol. sulphurous oxide. 4 vol. oxygen. Persulphuric oxide. Oxygen. When pure it is solid at ordinary temperatures, crystallizing sometimes in grains, sometimes in thin and flexible transparent needles. Sometimes it remains liquid. It is not stable, and decomposes spontaneously in about two weeks. When heated, it decomposes rapidly into sulphuric oxide and oxygen. S 2 7 2S0 3 -f O Persulphuric oxide. Sulphuric oxide. Water dissolves it with production of dense fumes and a brisk effervescence due to the disengagement of oxygen. The liquid then contains sulphuric acid. At the same time a small quantity of persulphuric acid, H 2 S 2 8 , or HSO, is formed, which soon decomposes into sulphuric acid and oxygen. This persulphuric acid, which is very unstable, would be analogous to permanganic acid ; its formation is expressed by the following equation : S'O 7 -f- H 2 ** 2HS0 4 SELENIUM AND TELLURIUM. Ill According to Berthelot, persulphuric acid is formed by the electrolysis of concentrated solutions of sulphuric acid. It would also be formed by the careful addition of a solution of hydrogen dioxide to sulphuric acid slightly diluted with water. 2H 2 S0 4 -f = H 2 -f 2HSO It is by no means certain that the formula HSO 4 represents the composition of a molecule of persulphuric acid. It is pos- sible that this formula must be doubled as indicated above. At present this point cannot be decided. SELENIUM AND TELLURIUM. These two rare elements present a great analogy to sulphur. Selenium was discovered by Berzelius in certain Swedish pyrites. Like sulphur, selenium has two allotropic forms, one crystalline, the other vitreous and amorphous. The crystalline variety begins to melt above 217, but liquefies only at 250 (Regnault) ; after rapid cooling it solidifies into a dark-brown mass. Its density is 4.8 when crystallized, and 4.3 when vit- reous. When heated in the air to a temperature above its melting-point it takes fire and burns with a blue flame, being converted into selenious oxide, SeO 2 . When sulphurous acid is added to a solution of selenious oxide the latter is reduced, sulphuric acid is formed, and the selenium is precipitated in the form of brown -red flakes. Its compound with hydrogen is a colorless gas having a fetid and irritating odor. Tellurium is still more rare than selenium ; it occurs com- bined with gold and other metals in certain minerals of Tran- sylvania and Hungary, and also in the Rocky Mountain gold region in the United States. It has the external appearance and the lustre of a metal. Its color is silvery-white ; its den- sity 6.25. It melts at about 500, and can be volatilized at a white heat in a current of hydrogen. It has a great tendency to crystallize. When heated in the air it burns with a green- ish-blue flame, forming tellurious oxide, TeO 2 . Its compound with hydrogen is a gas having an odor analogous to that of hydrogen sulphide. The following table shows the analogy between the principal compounds of sulphur, selenium, and tellurium : 112 ELEMENTS OF MODERN CHEMISTRY. H 2 S H 2 Se H 2 Te Hydrogen sulphide. Hydrogen selenide. Hydrogen telluride. SO 2 SeO 2 TeO 2 Sulphurous oxide. Selenious oxide. Tellurious oxide. SO 3 [SeO 3 ] TeO 3 Sulphuric oxide. Selenic oxide. Telluric oxide. [H 2 S0 3 ] H 2 Se0 3 H 2 Te0 3 Sulphurous acid. Selenious acid. Tellurious acid. H 2 SO H 2 SeO* H'TeO 4 Sulphuric acid. Selenic acid. Telluric acid. CHLORINE. Density compared to air 2.44 Density compared to hydrogen 35.5 Atomic weight Cl = 35.5 Chlorine was discovered by Scheele in 1774, and was first recognized as an element by G-ay-Lussac and Thenard in 1809, and by Sir Humphry Davy in 1810. Preparation. One part of manganese dioxide in coarse powder and six parts of common hydrochloric acid are intro- FIG. 38. duced into a flask fitted with a safety-tube and delivery-tube (Fig. 38). The reaction begins in the cold ; chlorine gas is CHLORINE. 113 disengaged, and may be collected over salt water. As soon as the disengagement of gas diminishes, it may be re-established by the application of a gentle heat. It is more convenient to collect the gas by dry displacement, and it may be obtained pure and dry by being conducted through a wash-bottle containing a small quantity of water, and a tube containing calcium chloride, as represented in the figure. It is then passed, by means of a tube bent at a right angle, into a dry jar. The chlorine being heavier than the air, col- lects at the bottom of the jar and gradually drives out the air, and the uniform greenish color of the whole of the gas in the jar indicates when the latter is completely filled. If it be desired to prepare a solution of chlorine in water, the gas may be passed through a series of Wolff's bottles con- FIG. 39. tain ing water, the contents of the first bottle being rejected, serving merely to wash the gas (Fig. 39). The reaction which takes place in the preparation of chlo- rine is a double decomposition between the manganese dioxide and the hydrochloric acid. Water and manganese chloride are formed, and chlorine is set free. MnO 2 -f 4HC1 == 2H 2 + MnCP + Cl 2 Manganese dioxide. Hydrochloric acid. Manganese chloride. Physical Properties. Chlorine is a greenish-yellow gas 10* 114 ELEMENTS OF MODERN CHEMISTRY. having a strong and suffocating odor. A litre of this gas weighs 3.16 gr. It may be liquefied at 15 by a pressure of four atmospheres. A small quantity of the liquid may easily be prepared in the following manner : Some crystals of chlorine hydrate are introduced into a tube of thick glass closed at one end and bent in the middle ; the other end is then hermetically sealed at the blast-lamp. The branch containing the crystals is then heated in a water-bath, while the other branch is cooled in a freezing mixture (Fig. 40). The hydrate of chlorine breaks up into water and chlorine, and the greater part of the latter is disen- gaged, and condenses by its own pressure into a deep-yellow liquid, which collects in the cooler limb of the tube (Faraday). Chemical Properties. One volume of water at 8 dissolves 3 volumes of chlorine ; at 17, 2.42 volumes. The saturated solution has a yellow color. When it is exposed to a tempera- ture of 0, it deposits crystals containing 27.7 per cent, of chlorine, and 72.3 per cent, of water, and constituting a hydrate of chlorine corresponding to the formula CP -\- 10H 2 (Fara- day). Chlorine possesses powerful affinities. It unites directly with the greater number of the other elements, and the com- bination frequently takes place with such energy that luminous heat is produced. Experiments. If powdered antimony or arsenic be sprinkled into a jar containing dry chlorine, each particle of the black powder burns with a bright spark as soon as it enters the atmos- phere of chlorine, producing thick, white fumes of antimony or arsenic chloride as the case may be. If a morsel of phosphorus, contained in a deflagrating spoon, be plunged into a jar of chlorine, the phosphorus melts and inflames spontaneously, and the sides of the jar become covered with a yellow, crystalline deposit of phosphorus pentachloride, PCI 5 . But the affinity of chlorine is most strikingly manifested by its action on hydrogen and hydrogen compounds. CHLORINE. 115 When a lighted taper is applied to a mixture of equal vol- umes of chlorine and hydrogen, the two gases unite instantly and explosively. Such a mixture will also explode violently on being exposed to direct sunlight ; the rays of the sun may even be replaced by the flame of magnesium or that of carbon disulphide. So great is the affinity of chlorine for hydrogen that it de- composes all hydrogen compounds, except hydrochloric and hydrofluoric acids. When it is dissolved in water, it slowly decomposes that liquid under the influence of sunlight, com- bining with the hydrogen and setting the oxygen at liberty. If a tube filled with an aqueous solution of chlorine be inverted over the pneumatic trough and exposed to direct sun- light, small bubbles of gas will be seen to rise through the liquid and collect at the top of the tube. This is the oxygen result- ing from the decomposition of the water. At a red heat, the vapor of water is rapidly decomposed by chlorine ; hydrogen sulphide gives up its hydrogen to chlorine at ordinary temperatures. All organic substances contain hydrogen ; they are therefore generally modified, and often destroyed by the action of chlorine. Coloring matters of organic origin are bleached. Experiment. If a solution of chlorine be added to a solu- tion of litmus, sulphate of indigo, or ink, the intense colors peculiar to these substances disappear, giving place to a pale yellow or brown tint. This effect is due to the more or less profound decomposition which these coloring matters undergo by reason of the removal of a certain portion of their hydro- gen in the form of hydrochloric acid. This bleaching property of chlorine is of great service in the arts. A wax taper will burn in chlorine gas with a red, smoky flame. The hydrogen of the wax combines with the chlorine, while the carbon is set free as smoke. A piece of paper satu- rated with oil of turpentine takes fire spontaneously when introduced into a jar of chlorine, producing a dense cloud of smoke ; the turpentine contains only carbon and hydrogen the latter is attacked by the chlorine, the former being set free. Chlorine is also an efficacious disinfectant. It decomposes hydrogen sulphide. It destroys odorous matters of organic origin, the effluvia resulting from putrid fermentation, and the miasms which are sometimes diffused in the air. It 116 ELEMENTS OF MODERN CHEMISTRY. is employed to disinfect privys, etc., and to purify the air in certain epidemics. The bleaching properties and disinfecting properties of chlorine are due to the same cause, its powerful affinity for hydrogen. HYDROCHLORIC ACID. Density compared to air 1.247 Density compared to hydrogen 18. Molecular weight HC1 = 36.5 Hydrochloric acid exists among the gaseous products disen- gaged by volcanoes. FIG. Preparation. Fragments of fused common salt are intro- duced into a flask fitted with a safety-tube and delivery-tube, like that for the preparation of chlorine, and concentrated sul- phuric acid is added. Hydrochloric acid gas is disengaged, and HYDROCHLORIC ACID. 117 may be collected over mercury. Sodium acid sulphate remains in the retort. H 2 S0 4 + NaCl = NaHSO* + HC1 Sodium chloride. Sodium acid sulphate. In the arts, the operation is conducted in cast-iron cylinders or furnaces (Fig. 41), at a high temperature. Under these conditions, one molecule of sulphuric acid acts upon two mole- cules of sodium chloride, yielding sodium neutral sulphate, and two molecules of hydrochloric acid. H'SO 4 -f 2NaCl = Na 2 S0 4 + 2HC1 Sodium sulphate. The hydrochloric acid gas evolved is passed into stoneware bottles, C, C', C'', containing water. It is thus dissolved, and the solution obtained constitutes the muriatic acid of com- merce. A solution of hydrochloric acid may be prepared in the laboratory by passing the gas through water contained in a series of Wolff bottles surrounded by cold water, the contents of the first bottle being rejected (Fig. 42). FIG. 42. Composition of Hydrochloric Acid. The composition of this gas may be deduced from the following experiments : 118 ELEMENTS OF MODERN CHEMISTRY. FIG. 43. 1. A bottle, B (Fig. 43), the neck of which is adapted by grinding with emery to the flask A, is filled with dry chlorine ; A, which has exactly the same capacity as the bottle, is filled with dry hydrogen ; the two vessels are then fitted together, and by means of the ground joint are hermetically sealed. The apparatus is now abandoned for a time to diffuse light, and as the two gases slowly mix they combine. The union is completed by exposing the apparatus to direct sunlight. When the tint of the chlorine has entirely disappeared, the two vessels are separated under the surface of mercury, and it is found that no change in volume has taken place. The chlorine and hydrogen have both disappeared to form hydrochloric acid, which occupies precisely the same volume as the two primitive gases. Consequently 2 volumes of hydrochloric gas contain 1 volume of chlorine and 1 volume of hydrogen ; and if the weight of one volume of hydrogen (unity) be added to that of one volume of chlorine (its density compared to hydrogen as unity), the sum will be the weight of two volumes of hydrochloric acid, and will also represent the weight of the molecule. Densities com- Densities com- pared to H. pared to Air. Weight of 1 volume of hydrogen .... 1 0.0693 Weight of 1 volume of chlorine .... 35.5 2.44 Weight of 2 volumes of hydrochloric acid 3(K5 2.5093 2. Two volumes of hydrochloric acid gas are passed into a bent tube over mercury (Fig. 44), and a small piece of sodium is passed up into the bulb and heated by the flame of a spirit- lamp. The sodium combines with the chlorine setting the hydrogen at liberty, and after the experiment one volume of hydrogen remains in the tube. This second experiment con- firms the first, both proving that hydrogen and chlorine unite in equal volumes, and without condensation, to form FIG. 44. HYDROCHLORIC ACID. 119 hydrochloric acid. One volume of hydrochloric acid contains half a volume of hydrogen and half a volume of chlorine, but we cannot admit that the atoms of these elements are divided into two in the formation of hydrochloric acid ; such a sup- position would be contrary to all ideas of atoms, which repre- sent the smallest particles of an element that can exist in a compound. It is more natural to conclude that two vol- umes of chlorine and two volumes of hydrogen react together in the formation of hydrochloric acid. Two volumes of chlorine contain two atoms, constituting one molecule of chlo- rine. In the same manner two volumes of hydrogen contain two atoms, constituting one molecule of hydrogen. Cl Cl H H volumes or 1 molecule of chlorine = CNJ1. 2 volumes or 1 molecule of hydrogen = HH. It is these molecules which are separated into two when chlorine combines with hydrogen : they exchange their atoms, and from the exchange, which is a double decomposition, there result two molecules of hydrochloric acid, which occupy pre- cisely the same volume as the two molecules of the simple gases. Cl Cl H H = H Cl H Cl 2 vols. of chlorine + 2 vole, of hydrogen r= 2 vols. of hydro- + 2 vola. of hydro- chloric acid chloric acid. We encounter here again the notion that certain elements in the free state are composed of molecules, each of which con- tains two atoms of the same kind. The force which unites them is not different from affinity. It is affinity which unites chlorine to chlorine in the molecule of that element ; hydrogen to hydrogen in the molecule of free hydrogen (Gerhardt). When, however, these two molecules are brought together, the affinity of chlorine for hydrogen preponderates, and brings about an exchange, a double decomposition. Physical Properties. Hydrochloric acid is a colorless gas having a pungent odor. It forms thick white fumes in the air by condensing the atmospheric moisture. It may be liquefied by a pressure of 40 atmospheres. It is one of the most soluble of gases in water. If a jar filled with this gas and inverted on a plate containing mercury 120 ELEMENTS OF MODERN CHEMISTRY. so that the mouth is sealed, be depressed in the pneumatic trough, and the plate be then quickly removed, the water im- mediately rushes into the jar as it would into a vacuum. The shock of the column of water is sometimes sufficient to break the jar. One volume of water at dissolves 500 volumes of hydro- chloric acid; at ordinary temperatures, about 480 volumes. The water becomes heated and increases in volume. The cold saturated solution has a density of 1.21 and contains 42.4 per cent, by weight of the dry gas. It is a colorless liquid, giving off white fumes. When it is heated, it loses a large quantity of the gas which it holds in solution, but the whole of the gas is not disengaged, and when the temperature reaches 110 the liquid distils without further loss of gas. A dilute hydrochloric acid is thus obtained, having a uniform density of 1.10 (Bineau). Chemical Properties. Hydrochloric acid is an energetic acid ; it strongly reddens litmus-paper. It is not decomposable by heat, but is partly decomposed by a series of electric sparks. AH of the metals which decompose water also decompose hy- drochloric acid with the liberation of hydrogen and the for- mation of a chloride. Such metals are sodium, zinc, iron, aluminium, tin, etc. Hydrochloric acid decomposes the metallic oxides and hy- drates with the formation of water and a chloride. If hydrochloric acid be added in small quantities to a con- centrated solution of potassium hydrate, the liquid becomes heated and deposits potassium chloride as a crystalline powder. HC1 -f KOH = KC1 -f H 2 O Potassium hydrate. Potassium chloride. Hydrochloric acid is then a true acid although it contains no oxygen, for it contains an atom of hydrogen that is replaceable by an atom of metal. In its action upon potassium hydrate it resembles nitric acid, for this acid also contains one atom of hydrogen, which is replaceable by an atom of metal. HNO 3 -f KOH = KNO 3 -f H 2 Nitric acid. Potassium nitrate. It is seen that the acids are compounds containing a strongly electro-negative atom or group of atoms, united with hydrogen, which hydrogen can be replaced by a metal. In nitric acid, H(N0 3 ), the group NO 3 plays the part taken by chlorine in OXYGEN COMPOUNDS OF CHLORINE. 121 hydrochloric acid ; like the chlorine, it renders the hydrogen replaceable by a metal. The action of hydrochloric acid upon the metallic oxides is analogous to that which it exerts upon the hydrates. If a current of hydrochloric acid be passed over mercuric oxide contained in a tube (Fig. 45), the oxide becomes heated, O FIG. 45. and is converted into a white powder which is mercuric chlo- ride ; at the same time water is formed and condenses in the bulb. HgO + 2HC1 = HgCP + H 2 Mercuric oxide. Mercuric chloride. OXYGEN COMPOUNDS OF CHLORINE. With oxygen, chlorine forms compounds which may be an- hydrous or hydrated ; the latter are acids. The oxides are : Hypochlorous oxide C1 2 Chlorous oxide C1 2 3 Chlorine peroxide C1 2 0* The acids are : Hypochlorous acid HC10 Chlorous acid HC10 2 Chloric acid HC10 3 Perchloric acid HC10 4 F 11 122 ELEMENTS OF MODERN CHEMISTRY. HYPOCHLOROUS OXIDE AND ACID. Hypochlorous oxide is prepared by passing a current of dry chlorine over mercuric oxide contained in a tube surrounded by cold water, and may be condensed in a long-necked matrass placed in a freezing mixture (Fig. 46). HgO -f 2CP == HgCP -f CPO Mercuric oxide. Mercuric chloride. FIG. 46. The oxide condenses as a brown-red liquid, boiling at 20. Above that temperature it is a reddish-yellow vapor, having a density of 2.977, or, compared to hydrogen as unity, 43.5. Two volumes of this vapor contain two volumes of chlorine and one volume of oxygen, a composition represented by the formula CPO. Hypochlorous oxide is a dangerous body, and cannot be kept for more than a few hours without spontaneous decomposition ; its vapor frequently explodes. In combining with the elements of water, hypochlorous oxide forms hypochlorous acid, the solution of which is almost color- less. ci + H ci + H CHLOROUS OXIDE. 123 Preparation of Hypochlorous Acid. 1. A solution of hypochlorous acid may be prepared by agitating mercuric oxide with water in jars filled with chlorine gas. The water will then contain hypochlorous acid and mercuric chloride, and there remains a brown powder, which is mercury oxychloride (Balard). 2. A current of chlorine is passed through water holding recently-precipitated calcium carbonate in suspension. The latter disappears, carbonic acid gas is disengaged, and the water becomes charged with calcium chloride and hypochlorous acid. The mixture is distilled, and the acid which passes with the water is condensed in a cooled receiver (Williamson). CaCO 3 + 2CP + H 2 == CO 2 + CaCP + 2HC10 Calcium Carbon Calcium Hypochlorous carbonate. dioxide. chloride. acid. Properties of Hypochlorous Acid. Concentrated hypo- chlorous acid is a dark-yellow liquid, having the peculiar smell of chlorinated lime or bleaching-powder. It is very caustic, and rapidly destroys the skin ; its bleaching power is very en- ergetic, double that of the chlorine it contains. Hydrochloric acid decomposes it into chlorine and water. HC10 + HC1 = CP + H 2 O CHLOROUS OXIDE. Chlorous oxide is formed when potassium chlorate is decom- posed by dilute nitric acid in the presence of a body capable of uniting with oxygen, such as arsenious oxide. At a gentle heat a greenish gas is disengaged which does not liquefy at a temperature of 20. This gas is not stable; above 57 it decomposes with explosion into chlorine and oxygen. It dissolves in water, forming a dark golden-yellow solution containing chlorous acid, a body quite unstable itself. CPO 3 + H 2 = 2HC10 2 Chlorous oxide. Chlorous acid. 124 ELEMENTS OF MODERN CHEMISTRY. CHLORINE PEROXIDE. Fia. 47. This compound, which was discovered by Sir Humphry Davy, is prepared by the ac- tion of concentrated sulphuric acid upon fused potassium chlorate. The salt is finely pulverized arid added in small quantities to sulphuric acid cooled to 10. The pasty mass is then introduced into a small test-tube fitted with a delivery-tube (Fig. 47), and is gently heated in a water- bath ; the gas disengaged is collected in dry jars by down- ward displacement. 3KC10 3 + 2H 2 SO* = KC10* + 2KHSO* + H 2 + CPO* Potassium Potassium Potassium acid chlorate. perchlorate. sulphate. Chlorine peroxide is a yellow gas having a sweetish aromatic odor. At 20 it condenses to an orange-red liquid. Its den- sity in the gaseous state is 33.75 (hydrogen being unity). This density is anomalous, and indicates that at the instant the liquid CPO* assumes the gaseous state it is dissociated into two more simple molecules, CIO 2 -f- CIO 2 , which occupy four volumes. is resolved into j f j The density of gaseous chlorine peroxide is then only half that required by the formula CPO*. If one volume of hydrogen weighs one volume of C1 2 4 ought to weigh But it weighs only oo.i./, which proves that CPO* in the gaseous state occupies volumes instead of two. These four volumes contain, 2 volumes of Cl, weighing 2 X 35.5 = 71 4 volumes of 0, weighing 16 X 4 == J54 135 Cl 2 0* Cl O 2 Cl O 2 1, 67.5. 33.75 four Weight of one volume, or density, compared to H -!L'_ 33.75 CHLORIC ACID PERCHLORIC ACID. 125 Chlorine peroxide is a dangerous body; it sometimes de- composes spontaneously with violent explosions. It is soluble in water, and the solution may be prepared by heating on a water-bath a mixture of equal parts of oxalic acid and potassium chlorate. Carbonic acid and chlorine peroxide gases are disengaged, and may be passed into water. Chlorine peroxide is absorbed by alkaline solutions with the formation of a chlorate and a chlorite. 2KOH -f CFO == KC10 3 + KC10* + IPO Potassium hydrate. Potassium chlorate. Potassium chlorite. CHLORIC ACID. HC10 3 This acid is formed by the spontaneous decomposition of solutions of hypochlorous and chlorous acids and chlorine per- oxide. It may be prepared by treating barium chlorate with dilute sulphuric acid. Barium sulphate precipitates, and is removed by filtration, and the solution of chloric acid is concentrated by evaporation in vacuo. Chloric acid is a syrupy liquid, ordinarily of a yellow color ; it is not very stable ; at a temperature of 40 it commences to decompose, and at a higher temperature it is resolved into per- chloric acid, chlorine, oxygen, and water. It has extremely energetic oxidizing properties ; when concentrated, it at once inflames sulphur, phosphorus, alcohol, and paper. It oxidizes sulphurous and phosphorous acids and hydrogen sulphide. With hydrochloric acid it forms water and chlorine. HC10 3 + 5HC1 = 3H 2 + 3CP PERCHLORIC ACID. HC10* This is the most rich in oxygen of all the chlorine acids, and it is a curious circumstance that it is also the most stable. It may be prepared by distilling potassium perchlorate with concentrated sulphuric acid. Roscoe obtains it by . distilling chloric acid, which is prepared by decomposing a solution of potassium chlorate by hydrofluosilicic acid. The insoluble po- ll* 126 ELEMENTS OF MODERN CHEMISTRY. tassium fluosilicate is separated by filtration, the filtered liquid is concentrated until white fumes appear, and then the distil- lation is commenced. The product must be rectified after being freed from the chlorine which is formed at the same time. The perchloric acid thus obtained is a heavy, oily, colorless liquid, resembling concentrated sulphuric acid. It still con- tains water, which may be removed by distillation with four times its weight of concentrated sulphuric acid. At about 100 dense vapors pass and condense into a very mobile, yellow liquid ; this is the perchloric acid HC10 4 ; the temperature then rises, and at 200 a liquid passes which solidifies to a crystalline mass on cooling. These crystals are a hydrate, HC10* + H 2 0. The pure or normal perchloric acid has a density of 1.782 at 15.5. When brought into contact with water, it combines with that liquid, producing a hissing noise. Its oxidizing powers are so energetic that it explodes on contact with paper, wood, or charcoal. It may be mixed with alcohol, but with ether it explodes. It cannot be distilled. The hydrate HC10* -f H 2 melts between 50 and 51. CHLORIDES OF SULPHUR. When a current of dry chlorine is passed over sulphur heated in a retort, a liquid condenses in the receiver which fumes in the air, has a yellow color, and an irritating, fetid odor. This is sulphurous chloride, S 2 CF. In order that this compound may be formed, the sulphur must be maintained in excess, and the operation must be stopped before it has all disappeared. The product is purified by rectification, that part being collected which passes at 139. When chlorine is passed for several hours through the chloride of sulphur just described, the yellow color of the latter changes to deep red. The liquid obtained is mobile, fumes in the air, and continually disengages chlorine. It can- not be distilled without decomposition. The product which passes is at first red, but afterwards assumes a lighter color, and when the temperature reaches 139 there remains in the retort only sulph*urous chloride, S 2 C1 2 . The red liquid has a composition which corresponds to the formula S 2 C1 4 . It is called perchloride of sulphur. Carius BROMINE. 127 regards it as a mixture of the chloride S 2 CP with a tetra- chloride SCI 4 , corresponding to sulphurous oxide. SO 2 sulphur dioxide. SCI* sulphur tetrachloride. This tetrachloride has been recently isolated by Michaelis, but it can only exist at a low temperature ; it decomposes into chlorine and sulphurous chloride, S 2 CP, as soon as it is removed from the freezing mixture where it has been condensed. The chlorides of sulphur are employed in vulcanizing caoutchouc. BROMINE. Vapor density compared to air . . . 5.393 Vapor density compared to hydrogen . 77.9 (nearly 80) Atomic weight Br =80. Bromine was discovered by Balard in 1826. Preparation. It is obtained by decomposing potassium bromide by manganese dioxide and sulphuric acid. Potassium sulphate and manganese sulphate are formed, and the bromine is liberated. 2KBr -f MnO 2 + 2H 2 S0 4 = K'SO* -f MnSO* + 2H 2 + Br 2 Potassium Manganese Potassium Manganese bromide. dioxide. sulphate. sulphate. The operation is conducted in a tubulated retort, heated on a sand-bath, and the bromine is condensed in a cooled receiver fitted to the retort by the aid of an adapter. The potassium bromide may be replaced by magnesium bromide, which exists in the mother-liquors of salt-springs. In this case magnesium sulphate is formed. The mother- liquors of the soda varech from which the iodine has Jbeen ex- tracted are also employed for the preparation of bromine. Properties. Bromine is a dark-red liquid, which solidifies at 7.3. Its density at 15 is 2.99. It boils at 63, and at ordinary temperatures gives off red, irritating vapors, for its vapor tension is considerable even in the cold. It stains the skin yellow, and immediately corrodes the tissues. It dissolves in about 33 times its weight of water at 15, forming an orange- red solution. At a low temperature it combines with water, forming a crystalline hydrate, Br 2 -j- 10H 2 0, analogous to that formed by chlorine. 128 ELEMENTS OF MODERN CHEMISTRY. Bromine dissolves in carbon disulphide, in chloroform, and in ether. Experiment. A small quantity of solution of potassium bromide is introduced into a long tube, closed at one end, and the tube is then nearly filled with chlorine- water ; when the two solutions are mixed, the liquor assumes an orange-red color from the liberation of the bromine. The tube is now filled up with ether and agitated briskly, the open end being closed with the finger. The ether passes through the aqueous solution and dissolves out all of the bromine, assuming at the same time a dark-red color. The affinity of bromine for hydrogen is powerful, but not as energetic as that of chlorine. Like chlorine, it has remarkable bleaching properties. HYDROBROMIC ACID. Density compared to air ......... 2.73 Density compared to hydrogen ...... 40.5 Molecular weight HBr ........ =81. Preparation. This gas is prepared by the action of water upon phosphorus tribromide. PBr 3 8 o == 3 3 + 3HBr Phosphorus tribromide. 3 molecules water. Phosphorous acid. The operation may be conveniently conducted in a doubly- curved tube (Fig. 48). Into the long branch CD fragments of phosphorus are introduced, carefully separated from each other by moistened broken glass. The bromine is introduced into the bend A. The shorter end is then corked, a delivery-tube adapted to the end D, and the bromine is gently heated until it boils. The vapor comes into contact with the phosphorus and forms phosphorus tribromide, but this is at once decomposed by the water into phosphorous acid and hydrobromic acid. The latter may be collected in jars over the mercury-trough. Amorphous phosphorus may be advantageously employed in this operation, and the process conducted as directed for hydri- odic acid (Personne). Properties. Hydrobromic acid is a colorless gas, producing dense white fumes in the air. A litre of this gas weighs 3.547 grammes. It liquefies at 73, and may be solidified at a lower temperature. It is formed by the union of equal volumes OXYGEN ACIDS OF BROMINE. 129 of bromine vapor and hydrogen without condensation, so that its composition corresponds to that of hydrochloric acid. It is very soluble in water ; its concentrated solution fumes in the air, and is very corrosive. Chlorine decomposes hydrobromic acid, setting free the bromine. Jb'io. OXYGEN ACIDS OF BROMINE. There are known three bromine oxygen acids : Hypobromous acid, HBrO. Bromic acid, HBrO 3 . Perbromic acid, HBrO 4 . They correspond to hypochlorous, chloric, and perchloric acids. Hypobromous Acid, HBrO. When mercuric oxide is agitated with an aqueous solution of bromine, a yellowish liquid is obtained which contains hypobromous acid, and can be distilled in vacuo. W. Dancer has obtained this acid by the action of bromine upon silver oxide suspended in water. 2Br* + Ag 2 -f H 2 = 2AgBr -f- 2HBrO Silver oxide. Silver bromide. In this process it is necessary to operate rapidly and avoid 130 ELEMENTS OF MODERN CHEMISTRY. the contact of an excess of silver oxide with the hypobromous acid, as the latter would be destroyed by the oxide with evolu- tion of oxygen. 2HBrO -f Ag 2 O = 2AgBr + H 2 -f O 2 The solution of hypobromous acid has a yellow color and bleaching properties analogous to those of hypochlorous acid. Bromio Acid, HBrO 3 . Potassium bromide and potassium bromate are formed by the action of bromine upon a concen- trated solution of potassium hydrate. This reaction is similar to that of chlorine upon potassa. Kammerer recommends the preparation of bromic acid by the action of chlorine upon bromine in presence of water. 5CP + Br 2 -f 6H 2 O = 10HC1 -f- 2HBr0 3 The hydrochloric acid is driven out by evaporation, and bromic acid remains in the form of a liquid that cannot be con- centrated to a syrupy consistence without partial decomposition. Perbromic Acid, HBrO 4 . Kammerer has obtained this acid by decomposing perchloric acid with bromine : chlorine is disengaged. After concentration on a water-bath, the per- bromic acid remains as a colorless oily liquid. It is relatively stable, as are the corresponding chlorine and iodine acids. Like them, it resists the reducing action of sulphurous acid and hydrogen sulphide. IODINE. Vapor density compared to air ... 8.716 Vapor density compared to hydrogen . 125.1 (nearly 127) Atomic weight I = 127. Iodine was discovered by Courtois in 1811, and was studied by G-ay-Lussac in 1813 and 1814. Natural State. Iodine is widely disseminated in nature. It is found in the mineral kingdom combined with various metals, such as potassium, sodium, calcium, magnesium, silver, mercury. The alkaline iodides exist in small quantity in sea- water, in a great number of salt-springs, and in certain rock- salts. The sodium nitrate found native in Chili contains traces of sodium iodate, and the mother-liquors from which the nitrate has been deposited contain enough iodate to be profitably employed for the preparation of iodine. The ashes of certain IODINE. 131 sea-plants, such as the algse and fuel, are the most abundant sources of iodine. Preparation. The ashes of sea-weeds, called kelp, are ex- hausted with water and the solution concentrated. Various salts, such as sodium and potassium sulphates and chlorides and sodium carbonate, are deposited, and the potassium iodide, which is contained in smaller quantity than these salts, remains in the mother-liquor. A regulated current of chlorine is passed into this solution as long as it continues to set free iodine, which is deposited as a pulverulent, black precipitate. An excess of chlorine must be avoided, as this would redissolve a portion of the iodine, forming iodine chloride. Another process consists in mixing the mother-liquor with ordinary nitric acid and gently heating the mixture. The alka- line iodide is decomposed by the acid, a nitrate is formed, red vapors are disengaged, and iodine is set free. 4HN0 3 + 2KI = 2KN0 3 -f 2N0 2 + 2H 2 + I 2 Nitric Potassium Potassium Nitrogen acid. iodide. nitrate. peroxide. The precipitated iodine is collected, drained, and after drying is sublimed in stoneware vessels. The same process that has been described for the manufacture of bromine from potassium bromide may also be applied for the extraction of iodine. It consists in treating the iodide with manganese dioxide and sulphuric acid. Properties of Iodine. The iodine obtained by sublimation occurs as scales or crystalline plates, having a brilliant, dark bluish-gray surface, and a density of 4.948 at 17. It may be obtained crystallized in rhombic octahedra by exposing to the air a solution of hydriodic acid. Iodine melts at 107. It boils at about 175, but volatilizes sensibly at ordinary temperatures. Its vapor has an intense rich violet color. A litre of this vapor weighs 11.32 grammes. Iodine is but very slightly soluble in water ; one part of iodine requires 7000 parts of water for its solution, but com- municates a light-brown color to the whole of that liquid. Alcohol and ether dissolve iodine freely, forming dark-brown solutions. Carbon disulphide, benzine, and chloroform also dissolve it, assuming a beautiful violet color. Experiment. If a few drops of chlorine-water be added to a very dilute solution of potassium iodide, the chlorine will 132 ELEMENTS OF MODERN CHEMISTRY. combine with the potassium, displacing the iodine, which will color the liquid brown ; if now the solution be agitated with a small quantity of chloroform, the latter will take up all of the iodine, assuming a violet color. Iodine strikes an intense blue color with starch. The reac- tion is very delicate and permits the detection of the smallest trace of free iodine. Experiment. If a few drops of a solution of potassium, iodide be added to a solution of starch, no coloration takes place, because the iodine is in combination ; but if a drop or two of chlorine-water be added, the iodine will be set free, and combining with the starch will at once produce the character- istic blue color. An excess of chlorine will again destroy the color. HYDRIODIC ACID. Density compared to air 4.443 Density compared to hydrogen 64.1 Molecular weight HI =128. Preparation. Hydriodic acid is prepared by the action of iodine upon phosphorus in presence of water; phosphorus triiodide is first formed, and this is decomposed into phos- phorous acid and hydriodic acid. |3 (. O3 _|_ QTTT ' : = : TTS r V -r oJtll Phosphorus 3 molecules Phosphorous triiodide. of water. acid. Amorphous phosphorus in powder is introduced into a glass- stoppered retort the neck of which is soldered to the delivery- tube (Fig. 49), and covered with a layer of water ; the iodine is then added, and on the application of a gentle heat a regular current of hydriodic acid is obtained. The gas may be col- lected, like chlorine, by downward displacement in dry jars. Properties. Hydriodic acid is a colorless gas producing white fumes in the air. It may be condensed to a yellow liquid by strong pressure or intense cold, and can even be solid- ified. Dry oxygen decomposes it at a high temperature, water being formed and the iodine being set at liberty. If a lighted taper be applied to a mixture of hydriodic acid and oxygen, the violet vapor of the iodine set free is instantly apparent. This decomposition of hydriodic acid by oxygen takes place at ordinary temperatures in the presence of water. A solution HYDRIODIC ACID. 133 of hydriodic acid exposed to the air rapidly becomes brown, and after a time deposits crystals of iodine. Solution of hydriodic acid is prepared by passing the gas into water cooled to 0. It may also be made by passing a current of hydrogen sulphide through water holding iodine in suspen- sion ; hydriodic acid is formed, and sulphur is precipitated. H 2 S -f F = 2HI -f S The saturated solution of hydriodic acid has a density of 1.7, and fumes in the air. When freshly prepared, it is color- FIG. 49. less ; when heated, it loses part of its gas, and finally distils unaltered at 126. The saturated solution contains 57.7 per cent, of the dry acid. Chlorine and bromine at once decompose hydriodic acid, combining with the hydrogen and setting free the iodine. The experiment may be made by pouring a few drops of bromine into a jar filled with hydriodic acid gas, when the appearance of a violet vapor immediately indicates the liberation of iodine. Potassium, zinc, iron, mercury, and silver decompose hydri- odic acid, but with unequal energies, setting free the hydrogen. 12 134 ELEMENTS OP MODERN CHEMISTRY. Sulphuric acid also decomposes it, and is itself reduced to sul phurous oxide. H 2 SO + 2HI = 2H 2 -f SO 2 -f I 2 Nitric acid is still more readily reduced by hydriodic acid. 2HN0 3 + 2HI = 2H 2 + 2N0 2 -f P Nitric acid. Nitrogen peroxide. IODINE OXIDES AND OXYGEN ACIDS. Among the compounds of iodine and oxygen, iodic and peri- odic oxides are the only ones known with certainty. The ex- istence of the other oxides, although possible and even probable, has not been fully demonstrated. These compounds would form the following series : Hypoiodous oxide IZQ lodous oxide I 2 3 Iodine peroxide * ... 1 2 0* Iodic oxide I2Q5 Periodic oxide PQ7 In combining with water, these oxides form acids ; it is only necessary to describe here iodic and periodic acids. TO 5 -f H 2 O == 2HI0 3 ,2 molecules iodic acid. PO 7 + H 2 == 2HI0 4 ,2 molecules periodic acid, IODIC ACID. HIO == I0 2 (OH) Iodic acid is formed when iodine is submitted to the action of energetic oxidizing agents, such as concentrated nitric acid or a mixture of nitric acid and potassium' chlorate. It is also formed by the action of an excess of chlorine on iodine in presence of water. p + 5CP -|- 6H 2 == 10HC1 -f 2HI0 3 Preparation. Iodic acid may be conveniently prepared by heating iodine and potassium chlorate with dilute nitric acid. The oxygen of the chlorate oxidizes the iodine to iodic acid, and on adding barium nitrate to the liquid, barium iodate is precipitated. The latter salt is decomposed by sulphuric acid ; iodic acid is set free in the solution, and barium sulphate is precipitated ; the filtered solution is concentrated by evapora- tion in vacuo. Properties. Iodic acid is solid, and crystallizes in hex- agonal tables. When heated to 170 it loses water and is PERIODIC ACID. 135 converted into iodic oxide, and at a red heat the latter is decomposed into iodine and oxygen. It is seen that iodic acid is much more stable than its ana- logue, chloric acid ; nevertheless it is easily reduced by bodies avid of oxygen. If sulphurous acid be added to a solution of iodic acid, a precipitate of iodine is formed instantly, but an excess of sul- phurous acid redissolves the precipitate, part of the water being decomposed and hydriodic and sulphuric acids being formed. Iodic acid is also decomposed by hydriodic acid. If a solu- tion of iodic acid be poured into a solution of starch, no color- ation appears, but the characteristic blue color is at once developed on adding a drop of hydriodic acid. HIO 3 + 5HI = 3H 2 + 3P PERIODIC ACID. This acid has been obtained from disodic periodate, a salt which is precipitated when a current of chlorine is passed through a solution of sodium iodate mixed with sodium hydrate. NalO 3 + 3NaOH + CP = I0 5 j^Vo + 2NaCl Sodium iodate. Sodium hydrate. Disodic periodate. Sodium chloride. The crystalline precipitate is dissolved in nitric acid, and lead nitrate is added to the solution ; lead periodate is precipi- tated, and this salt is exactly decomposed by sulphuric acid ; the liquid is filtered to separate the lead sulphate, and evapo- rated at a gentle heat. The periodic acid crystallizes out in colorless, deliquescent, rhombic prisms, fusible at 130. These crystals contain H 3 I0 5 -f H 2 0. At 160 they lose water and are converted into a white mass of periodic oxide. 2(H 3 I0 5 .H 2 0) = PO T + 5H 2 Between 180 and 190 periodic oxide abandons oxygen, and is converted into iodic oxide, I 2 5 . Periodic acid forms several varieties of salts. There is a diargentic periodate, I0 5 j jj^,H 2 = ~t~ H2() ' corres P ndin g to the disodic salt before mentioned; but there is also a silver periodate, AglO 4 , to which corresponds an acid, HIO*, having a composition analo- gous to that of perchloric acid, but which has not yet been obtained. 136 ELEMENTS OP MODERN CHEMISTRY. Analogy between Chlorine, Bromine, and Iodine. Chlo- rine, bromine, and iodine present a striking analogy in their chemical properties, and this analogy is seen in all of their compounds. They combine with hydrogen, atom for atom, forming the acids HC1 HBr HI and it is seen that the atoms of chlorine, bromine, and iodine are equivalent to each other and to an atom of hydrogen ; each of these elements is monatomic. Their affinities for hydrogen are far from being equal ; in this respect chlorine is more powerful than bromine, and bromine than iodine. The contrary has been noticed regarding their affinities for oxygen, for the oxygen acids of iodine are more stable than those of chlorine. The analogy between these three elements is followed out in the constitution of their oxides and acids, and in their com- binations with the metals. The chlorides, iodides, and bro- mides possess in general the same constitution, and it is to be remarked that the greater part of these binary compounds are soluble in water and are crystallizable like salts, of which they otherwise present the characters. Hence the name halogen bodies, which was applied by Berzelius to this group of elements, to indicate that they form salts in combining with the metals. FLUORINE. Fl = 19. This is a body belonging to the same group just considered, and having a chemical energy much superior to that of chlorine. It exists in the common mineral fluor spar, which is a combina- tion of fluorine and calcium. But fluorine has never been isolated ; it attacks all vessels, and it would be necessary to have apparatus and vessels cut from fluor spar in order to con- tain it. There is a compound of fluorine and hydrogen. HYDROFLUORIC ACID. Molecular weight HF1 =20 This compound is prepared by decomposing powdered cal- cium fluoride with sulphuric acid. CaFP + H'SO* = CaSO* + 2HF1 Calcium fluoride. Calcium sulphate. HYDROFLUORIC ACID. 137 The operation is conducted in a leaden retort, to which is adapted a receiver of the same metal surrounded by a freezing mixture (Fig. 50). The hydrofluoric acid condenses as a very acid liquid, which fumes strong- ly in the air. Its density is LOG. In this state it still re- tains water ; but Fremy obtained it ^f anhydrous by de- Ig composing dry hy- drofluoride of fluor- ide of potassium, Jb'io. 50. KF1,HF1, by heat in a platinum retort. This salt breaks up into potassium fluor- ide, which remains, and hydrofluoric acid, which is disengaged and must be condensed in a platinum receiver cooled to 20. Pure and anhydrous hydrofluoric acid is liquid at ordinary tem- peratures ; it is very mobile, and boils at 19.4 (Gore). It is extremely corrosive, and manipulations with it should be con- ducted with great care. Its affinity for water is so great that each drop of the acid let fall into that liquid produces a hissing noise, as would a red-hot iron. The solution is employed for etching upon glass, for hydrofluoric acid attacks and corrodes that substance. This effect is due to the action of the acid upon the silica of the glass, which it converts into either sili- con fluoride or hydrofluosilicic acid, as will be seen farther on. FIG. 51. A design may readily be engraved on glass by covering the glass with a thin coating of wax, through which the design is 12* 138 ELEMENTS OF MODERN CHEMISTRY. traced with a sharp point ; the glass is then placed over a leaden capsule containing a mixture of powdered calcium fluoride, and sulphuric acid (Fig. 51), which is gently heated by a spirit-lamp. Hydrofluoric acid vapor is disengaged and attacks the glass wherever it is not protected by the wax. When the wax is re- moved, the design is found to be permanently etched on the glass. A dilute solution of hydrofluoric acid or a bath of hydro- fluoride of potassium fluoride may be employed instead of the vapor in the former experiment, but in this case the etched portions are transparent and not opaque as when produced by the vapor ; they may be rendered opaque by adding a salt, such as potassium or ammonium sulphate, to the bath. NITROGEN. Density compared to air 0.9714 Density compared to hydrogen 14.1 Atomic weight N = 14. Nitrogen is one of the elements of the air, and it was from air that it was first obtained in a pure state by Lavoisier and Scheele, in 1777. To obtain nitrogen from the atmosphere it is only necessary to remove the other element, oxygen. Preparation. A flat piece of cork, B (Fig. 52), floating in the pneumatic-trough, supports a small capsule containing a fragment of phos- phorus. The latter is inflamed, and the capsule immediately covered with a bell- jar. The heat pro- duced by the com- bustion at first ex- pands the air and drives out a portion, but in a few minutes the water rises in -riE the jar, taking the place of the oxygen FIG. 52. which has been con- sumed. When the phosphorus is extinguished, the experiment has terminated. The water gradually dissolves the white smoke of phosphoric oxide which fills the jar, and there remains a colorless, irre- AMMONIA. 139 spirable gas that will not support combustion. This gas is nitrogen, still mixed with traces of oxygen and carbonic acid gas. Pure nitrogen may be obtained by passing a current of air, previously freed from moisture and carbon dioxide, through a porcelain tube containing incandescent copper. The copper absorbs the oxygen, and pure nitrogen passes out at the end of the tube and may be collected over the pneumatic trough. Pure nitrogen may also be obtained by heating ammonium nitrite in a glass retort ; heat decomposes this salt into nitrogen and water. (NH 4 )N0 2 = 2H 2 -f N 2 Ammonium nitrite. Properties. Nitrogen is a colorless gas, somewhat lighter than the air. A litre of this gas weighs 1.257 grammes. It extinguishes burning bodies, and is not combustible itself; it produces no precipitate in lime-water. Water dissolves only fa of its volume of nitrogen at 0. Animals are quickly suffo- cated in an atmosphere of pure nitrogen, but the gas does not exert a poisonous influence upon the economy. The affinities of nitrogen are not energetic. It combines directly with only a very small number of elements, among which may be mentioned carbon, silicon, boron, arid titanium. Under the influence of a series of electric discharges it will unite with oxygen, forming nitrogen peroxide ; with hydrogen, forming ammonia. AMMONIA. Density compared to air 0.596 Density compared to hydrogen 8.60 Molecular weight NH 3 = 17. Ammonia was discovered by Priestley, studied by Scheele, and analyzed by Bertholet in 1785. Preparation. Equal weights of quick-lime and sal am- moniac, both in powder, are rapidly mixed in a mortar, and the mixture introduced into a glass flask, which is then filled up with fragments of quick-lime. A cork and delivery-tube are adapted to the flask, which is then gently heated and the gas disengaged collected over mercury. The calcium oxide or lime decomposes the ammonium chloride (sal ammoniac), with the formation of calcium chloride, ammonia gas, and water ; the latter is absorbed by the fragments of lime which fill up the flask. 2NH 4 C1 + CaO == 2NH 3 -f CaCP -f H 2 Ammonium chloride. Calcium oxide. Ammonia. Calcium chloride. 140 ELEMENTS OF MODERN CHEMISTRY. A solution of ammonia in water may be prepared by passing the gas through a series of Wolff's bottles, about half filled with water, excepting the first, which should only contain a small quantity destined to wash the gas. Physical Properties. Ammonia is a colorless gas, having a powerful and pungent odor, which excites tears. Its taste is burning and caustic. It may be liquefied by a temperature of 40, or at 10 under a pressure of 6 atmospheres. Fara- day's method of liquefying it is as follows : ammonia is passed over dry silver chloride, by which it is absorbed. The silver chloride, saturated with ammonia, is introduced into a bent tube (Fig. 53), the empty limb of which is then sealed at the FIG. 53. Fio.54. blow-pipe. The end containing the chloride is now heated in a water-bath, while the empty end is cooled in a freezing mix- ture (Fig. 54). The ammonia is driven out from the silver chloride, and condenses into a transparent liquid in the cooler branch. Faraday succeeded in solidifying ammonia by subject- ing this liquid to rapid evaporation. In the solid state it is a white, crystalline, transparent substance, fusible at 75, and having only a feeble odor. According to Bunsen, liquid ammo- nia boils at 35 under a pressure of 0.7493 metre ; its density is 0.76. Ammonia gas is very soluble in water, which dissolves 1000 times its volume at 0, and about 740 times its volume at 15. The rapid absorption of ammonia by water may be strik- ingly shown by the following experiment. A bottle, A (Fig. 55), is filled with ammonia gas, and fitted with a cork, through which passes a tube drawn out at both extremities, and the outer end of which is sealed. If this end be plunged under water and the point be broken off, the water at once rises into AMMONIA. 141 the bottle, forming a fountain, and the vessel becomes filled with water in a very short time. The aqueous solution of ammonia possesses the odor of the gas ; it is caustic, and was formerly called vol- atile alkali and spirits of hartshorn. It is largely used in the arts and as a reagent. Its density is 0.855. When heated, it loses ammonia gas, the whole of which may be driven out by boiling. Composition of Am- monia, 200 volumes of ammonia gas are in- troduced into an eudi- ometer, and electric sparks are passed through the gas for some time by means of a Ruhmkorff coil (Fig. 56). When the experiment has terminated, the volume of gas will be found to have doubled. 200 volumes of oxygen are added to the 400 volumes of gas thus obtained, and a spark is passed; an explosion takes place, and after making the Fio. 55. FJG. 56. necessary corrections for temperature and pressure, the 600 volumes of gas are found to be reduced to 150 volumes ; 450 volumes have thus disappeared to form water. 142 ELEMENTS OP MODERN CHEMISTRY. These 450 volumes must have contained 300 volumes of hydrogen, 150 volumes of oxygen. Consequently the 200 volumes of ammonia gas, which were decomposed by the spark into 400 volumes, must have been formed by the union of 300 volumes of hydrogen, 100 volumes of nitrogen. The latter gas remains in the eudiometer, together with the 50 volumes of oxygen that were employed in excess. From this analysis it is seen that two volumes of ammonia contain three volumes of hydrogen and one volume of nitrogen, a composition which is expressed by the formula NH 3 . Chemical Properties. Ammonia gas is decomposed by a high temperature, as by a series of electric sparks. The experi- ment may be made by passing the gas through a porcelain tube FIG. 57. filled with fragments of broken porcelain and heated to white- ness, and collecting the gas resulting from the decomposition in vessels filled with water (Fig. 57). This gas is found to be a mixture of three volumes of hydrogen and one volume of nitrogen. The decomposition takes place more readily if iron, copper, or platinum wires be introduced into the porcelain tube. AMMONIA. 143 latter metal is not altered, but the iron and copper become brittle and retain a few per cent, of nitrogen. The decompo- sition of the ammonia seems here to be favored by the forma- tion of metallic nitrides, unstable compounds which are almost entirely decomposed by the prolonged action of the heat. Ammonia gas will not burn in the air, but a mixture of four volumes of ammonia and three volumes of oxygen will explode on the application of a flame. 2NH 3 + O 3 = 3H 2 + N 2 Ammonia will burn in an atmosphere of oxygen. A jet of ammonia escaping through a tube drawn out to a point may be ignited on the instant that it is plunged into a jar of oxygen, and will continue to burn with a yellowish flame until the oxygen is consumed (Fig. 58). Independently of this rapid combus- tion, ammonia may undergo a slow com- bustion under the fol- lowing conditions : The vessel A (Fig. 59) contains a solution of ammonia, above which is suspended a spiral of platinum wire. The solu- tion is gently heated, and a rapid current of oxygen gas is forced through it. The mixed ammonia and oxygen gases come in contact with the platinum spiral and combine together, their union developing so much heat that the spiral is heated to redness. The vessel sometimes becomes filled with white fumes of ammonium nitrite. The nitrous acid is produced by the slow oxidation of the ammonia. If a mixture of oxygen and ammonia gases be passed through a heated tube contain- ing spongy platinum, nitric acid and water will be formed and disengaged in vapor. Action of Chlorine and Iodine upon Ammonia. Chlorine instantly decomposes ammonia, combining with its hydrogen. If a drawn-out tube through which a jet of ammonia is escaping FIG. 58. 144 ELEMENTS OF MODERN CHEMISTRY. be plunged into a bottle filled with dry chlorine (Fig. 60), the ammonia takes fire immediately, and white vapors of ammo- nium chloride are formed. 4NH 3 -f CP == 3NH 4 C1 -f N If a long tube closed at one end be almost entirely filled with saturated chlorine water and then filled up with a solu- tion of ammonia, and quick|y inverted on the pneumatic trough, the lighter solution of ammonia will rise through the chlorine-water and will be de- composed according to the pre- ceding equation. Ammonium chloride will remain in solution, while the nitrogen will collect at the top of the tube. Nitrogen Chloride. Under other conditions the nitrogen may combine with the chlorine, forming a very explosive and dangerous compound, nitrogen chloride. This experiment may be made as follows : A small jar of chlo- rine is inverted in a saucer con- taining a solution of ammonium chloride. The ammonia of this salt is slowly decomposed by the chlorine, with the for- mation of hydrochloric acid and nitrogen chloride. As the chlorine is absorbed, the level of the liquid in the jar rises and a drop of a yellow liquid soon collects on the surface. A light tap on the vessel causes it to sink through the solution into the saucer. This oily body is nitrogen chloride. The jar may now be removed and a small piece of phosphorus thrown into the saucer, and pushed from a distance towards the drop of nitrogen chloride by the aid of a long wooden rod. FIG. 59. FIG. 60. AMMONIA. 145 As soon as the two substances come into contact, the nitrogen chloride explodes and the saucer is broken into pieces. The formula NCF has been attributed to this body. Nitrogen Iodide. There is another explosive compound analogous to nitrogen chloride, but containing iodine. It is obtained as a black powder by treating powdered iodine with ammonia; when dry it explodes with great violence on the lightest touch, and sometimes spontaneously. Bunsen has attributed to it the formula N 2 HT. According to Stahlschmidt, the composition of nitrogen iodide corresponds to the formula NF, when this body is pre pared by the action of an alcoholic solution of iodine upon aqueous ammonia ; but if both bodies be in alcoholic solution, an iodide is obtained having the formula NHP. If this be correct, these bodies present very simple relations with ammonia. ci ri ri K-.i Nil N H N Cl -. (H (ci (i (H Ammonia. Nitrogen chloride. Triiodammonia. Diiodammonia. Trichlorammonia. Nitrogen iodides. The substitution of the chlorine or iodine for hydrogen takes place atom for atom. Action of Potassium upon Ammonia. When potassium is heated in an atmosphere of ammonia, the brilliant surface of the metal becomes covered with a greenish-black liquid, and at the same time hydrogen is disengaged. The metal entirely disappears little by little, and, on cooling, the liquid solidifies to an olive-green mass. This substance represents ammonia in which one atom of hydrogen has been replaced by an atom of potassium. H) K) H V N = Ammonia. H }- N = Potassium amide. HJ HJ When it is treated with water, ammonia is regenerated and potassium hydrate is formed. KNH 2 + H 2 == KOH + NH 3 Potassium amide. Potassium hydrate'. Ammonium Amalgam. If liquid amalgam of potassium or sodium and mercury be treated with a saturated solution of ammonium chloride, the amalgam increases in volume, assumes a buttery consistence, and is converted into a soft, light mass G 13 146 ELEMENTS OF MODERN CHEMISTRY. having the metallic lustre of mercury. It will retain the impression of the finger and will float upon water; but it gradually decomposes, losing hydrogen and ammonia, and only mercury remains. This unstable body is called ammonium amalgam. In it the mercury is combined with a group, NH 4 , which contains all of the hydrogen of the ammonium chloride, the chlorine of which has combined with the potassium. NH :! .HC1 Cl = NH* Ammonium chloride. Radical ammonium. It has recently been found that the ammonium amalgam is very compressible, and that its diminution in volume under pressure sensibly follows Mariotte's law. It has hence been concluded that the ammonium does not exist in combination with the mercury, and that the increased volume of the latter is due simply to an absorption of gas. It is difficult to admit this, for the compressibility of the ammonium amalgam proves only that the compound has no stability, and begins to decom- pose almost immediately on its formation. The disengaged gases, which are in the exact proportion NH 3 -f- H, may be retained by the pasty amalgam remaining : they could not be absorbed by the liquid mercury. Ammonium Theory. The reaction which has just been described is of great importance, and directly supports the ammonium theory suggested by Ampere. According to this theory, the ammoniacal salts are analogous in constitution to ordinary salts, from which they differ only by the substitution of a compound radical, ammonium, for a simple radical. The following formulae explain this proposition : NH 3 .HC1 = (NH*)C1 analogous to KC1 Ammonium chloride. Potassium chloride. NH 3 .HN0 3 = (NH 4 )N0 3 analogous to KNO 3 Ammonium nitrate. Potassium nitrate. NH 3 .H 2 S = g S analogous to S Ammonium sulphydrate. Potassium sulphydrate. (NH 3 ) 2 .H 2 S ^ | S analogous to | j S Ammonium sulphide. Potassium sulphide. AMMONIUM CHLORIDE. NH*C1 This salt was formerly obtained from Egypt, where it was made by subliming the soot produced by the combustion of AMMONIUM SULPHYDRATE AND AMMONIUM SULPHIDE. 147 camel's dung. It is now prepared in large quantities from gas- liquor, or the water condensed in the manufacture and purifi- cation of illuminating gas from coal. This liquor is heated with lime, ammonia is disengaged and is conducted into hydro- chloric acid. Ammonium chloride is obtained by simply evaporating the solution. It is purified by sublimation in stoneware pots which are heated in a furnace out of which the upper parts of the pots project. There the volatilized chloride condenses, and the sublimed product is known in commerce as sal ammoniac, or muriate of ammonia. It generally occurs as white or grayish, compact masses, having a crystalline fibrous structure. Its taste is sharp and salty. It dissolves in two and a half parts of cold, and in its own weight of boiling water. It is deposited from a satu- rated solution in small octahedra, grouped together in needles, and presenting a fern-leaf-like appearance. At a high tem- perature it volatilizes without melting and sublimes without decomposition. Ammonium chloride is formed by the union of equal vol- umes of hydrochloric acid and ammonia gases. AMMONIUM SULPHYDRATE AND AMMONIUM SULPHIDE. Hydrogen sulphide and ammonia gases unite in the cold in two different proportions, forming two compounds, ammo- nium sulphydrate and ammonium sulphide. H 2 S -f NH 3 Hyrogen sulphide. Ammonia. Ammonium sulphydrate. (2 vol.) (2 vol.) IPS -f 2NH 3 Hydrogen sulphide. Ammonia. Ammonium sulphide. (2 vol.) (4 vol.) These compounds are definite, but are decomposed into their elements by heat. Horstmann and Salet have shown that hy- drogen sulphide and ammonia gases may be mixed in all pro- portions without contraction in volume taking place, provided the temperature be maintained above 60. Ammonium sulphydrate is generally obtained in solution by saturating aqueous ammonia with hydrogen sulphide. This solution is colorless, but acquires a yellow color on exposure to 148 ELEMENTS OP MODERN CHEMISTRY. the air. When a quantity of ammonia is added to it equal to that which it already contains, ammonium sulphide, (NH*/S, is formed, which corresponds to potassium sulphide, K 2 S. Ammonium sulphide is largely employed in the laboratory as a reagent for the detection of certain metals. If ammonium sulphide be added to a solution of ferrous sulphate, a double decomposition takes place ; ammonium sul- phate is formed and remains in solution, while ferrous sulphide forms a black precipitate. FeSO + (NH*) 2 S = FeS -f (NH*) 2 SO Ferrous sulphate. Ferrous sulphide. Ammonium sulphate. The salts of zinc, manganese, cobalt, and nickel are likewise precipitated as sulphides by ammonium sulphide. The salts of aluminium and chromium are precipitated as hydrates, hydrogen sulphide being disengaged. The preceding salts are not precipitated by hydrogen sul- phide (the zinc salts are not precipitated if they be acid), but the latter reagent precipitates in the form of sulphides the salts of lead, bismuth, copper, cadmium, mercury, silver, antimony, tin, gold, and platinum. The sulphides of the latter four metals dissolve in an excess of ammonium sulphide. The sulphides of arsenic, tin, antimony, gold, and platinum all form compounds with ammonium sulphide, in which the latter plays the part of a base. AMMONIUM NITRATE. (NH)NO* Ammonium nitrate is prepared by saturating nitric acid with ammonia. It crystallizes in large, transparent, fusible prisms, which are very soluble in water and produce a notable depression of temperature in the act of solution, extending even to 15. At 300 ammonium nitrate is decomposed into nitrogen monoxide and water. It is used for the prepa- ration of nitrogen monoxide, much used as an anaesthetic. AMMONIUM CARBONATE. When dry carbon dioxide and ammonia gases are mixed in the proportion of 2 volumes of the first to 4 volumes of the second, they condense, forming a white powder, which is am- AMMONIUM SULPHATE HYDEOXYLAMINE. 149 monium carbamate, a compound which was formerly called anhydrous carbonate of ammonia. CO 2 -f- 2NH 3 = Ammonium carbamate. The ammonium carbonate of commerce is generally consid- ered as a sesquicarbonate. It contains 2[C0 2 (NH 4 ) 2 ] + CO 2 + 2H 2 0. It is obtained by heating a mixture of equal parts of ammonium sulphate and chalk in a subliming apparatus. Ammonia and water are disengaged, and the sesquicarbonate of ammonium sublimes. Recently sublimed ammonium sesquicarbonate is transparent and crystalline. It has a strong ammoniacal odor and a sharp caustic taste. When exposed to the air it gradually loses ammonia and is converted into ammonium acid carbonate. Ammonium Acid Carbonate. This salt, which is com- monly known as bicarbonate of ammonia, may be obtained by passing a current of carbonic acid gas into aqueous ammonia, to saturation. The acid salt is deposited in right rhombic prisms. The neutral carbonate of ammonium is not known. These salts present the following relations to the hypothetical carbonic acid : OH OH ONH< Carbonic acid. Ammonium acid Ammonium (Hypothetical.) carbonate. carbonate. AMMONIUM SULPHATE. (NH<) 2 SO* This salt is obtained in the arts by passing the ammonia that is disengaged when gas-liquor is heated with lime into dilute sulphuric acid. It crystallizes in right rhombic prisms. It is colorless and has a sharp taste. It dissolves in two parts of cold, and in its own weight of boiling, water. It is insoluble in alcohol. HYDROXYLAMINE. NH*(OH) This remarkable compound was discovered by Lossen. It is formed when ethyl nitrate is reduced by tin and hydrochlo- ric acid. It is also a product of the action of dilute nitric acid upon tin, and that of hydrochloric acid and tin upon ammo- nium nitrate. 13* 150 ELEMENTS OF MODERN CHEMISTRY. Finally, Lessen has prepared it synthetically by passing a current of nitrogen dioxide over tin moistened with hydro- chloric acid, which determines a disengagement of hydrogen. 2NO + 3H 2 = 2[NH' 2 (OH)] In the first reactions the nitric acid is reduced by the hy- drogen resulting from the action of a dilute acid upon tin, and which is then, just as it is set free, in what is called the nascent state. HNO 3 + 3H 2 = 2H 2 + NH 2 .OH Nitric acid. The hydroxylamine thus formed remains in the liquid com- bined with an excess of acid. It possesses the properties of an energetic base. It forms definite salts with the acids, and can be regarded as ammonia, in which the group OH (hydroxyl) has been substituted for one atom of hydrogen. N 1 H H (OH N } H Ammonia. Hydroxylamine. Thus far it has not been isolated ; when a solution of potas- sium hydrate is added to a concentrated solution of a salt of hydroxylamine, nitrogen is disengaged and ammonia is formed. 3(NH 2 .OH) = N 2 -f NH 3 -f 3H 2 Lossen has obtained an aqueous solution of hydroxylamine by decomposing a dilute solution of hydroxylamine sulphate with the exact quantity of baryta- water sufficient to precipitate the sulphuric acid. Hydroxylamine possesses reducing properties ; it precipi- tates copper and mercury in the metallic state from solutions of their salts. OXYGEN COMPOUNDS OF NITROGEN. Five compounds of nitrogen and oxygen are known. ATOMIC COMPOSITION. VOLUMETRIC COMPOSITION. Nitrogen monoxide, or nitrous oxide ........ N 2 2 vol. N and 1 v. condensed in 2 v. Nitrogen dioxide ..... NO 1 vol. N and 1 v. = 2 v. Nitrogen trioxide .... N 2 3 2 vol. N and 3 v. condensed in 2 v. Nitrogen tetroxide, or nitrogen peroxide ....... N 2 0* 2 vol. N and 4 v. condensed in 2 v. Nitrogen pentoxide, or nitric anhydride ...... N 2 5 2 vol. N and 5 v. condensed in 2 v. NITROGEN MONOXIDE. 151 Nitrogen trioxide and nitrogen pentoxide combine with water, forming nitrous and nitric acids. N 2 3 + H 2 == 2HN0 2 Nitrogen trioxide. Nitrous acid. N 2 5 _|_ JJ2Q = 2HN0 3 Nitrogen pentoxide. Nitric acid. NITROGEN MONOXIDE. Density compared to air 1.527 Density compared to hydrogen 22. Molecular weight N2Q = 44. This gas, known also as protoxide of nitrogen, nitrous oxide, and laughing-gas, was discovered by Priestley in 1776. Preparation. It is obtained by gently heating ammonium nitrate in a glass retort. The salt melts, and then decomposes FIG. 61. with effervescence into water and nitrogen monoxide, which may be collected over water (Fig. 61). (NH*)N0 3 = N 2 + 2H 2 Properties. Nitrogen monoxide is colorless and odorless, but possesses a sweetish taste. It is not permanent, and may be liquefied by strong pressure. It is liquefied on a consider- able scale at present, that it may be transported in small bulk for the use of dentists. For this purpose it is compressed in strong iron reservoirs. A remarkable experiment can be performed as follows : A quantity of liquid nitrogen monoxide is poured into a test-tube fixed by a cork in the neck of a bottle ; a portion of it instantly volatilizes, producing intense cold. If now a little mercury be poured into the tube, it will sink through the liquid monoxide and immediately be solidified. A small piece 152 ELEMENTS OF MODERN CHEMISTRY. FIG. 62. of incandescent charcoal let fall into the tube will float upon the surface of the monoxide, and burn with great brilliancy, notwithstanding the intense cold by which it is surrounded, as evi- denced by the freezing of the mercury (Fig. 62). Water dissolves about its own volume of nitrogen monoxide at ordinary temperatures. A taper which has been extin- guished, but still bears a spark of fire, is relighted, and burns brilliantly when plunged into a jar of nitrous oxide (Fig. 63). In the same manner, the combustion of sulphur and phos- phorus is effected with great energy in an atmosphere of this gas. Equal volumes of nitrous oxide and hydrogen form a mixture which explodes on the passage of an electric spark or on the application of flame. N 2 -f- H 2 = H 2 + N 2 2222 volumes, volumes, volumes, volumes. Respiration is a slow com- bustion and may be sustained for a few seconds by nitrogen monoxide. Such inhalation does not suffocate but it dis- turbs the functions of the nervous system, producing anaesthesia, and for this pur- pose nitrous oxide is now largely employed by surgeons and dentists. The insensibility is frequently preceded by a stage of intoxication, hence the name laughing-gas, which was given by Davy. It must be added that these exhilarating effects have not been observed in recent experiments upon perfectly pure nitro- gen monoxide. FIG. 63. NITROGEN DIOXIDE, OR NITRIC OXIDE. 153 NITROGEN DIOXIDE, OR NITRIC OXIDE. Density compared to air 1.039 Density compared to hydrogen 15. Molecular weight NO =-30. Preparation. This gas was discovered in 1*7 72 by Hales ; it is prepared by decomposing cold, dilute nitric acid by metallic copper. 3Cu -f 8HNO 3 = 3Cu(N0 3 ) 2 + 4H 2 + 2NO Copper. Nitric acid. Cupric nitrate. The copper and water are introduced into a gas-bottle, and ordinary nitric acid is added by means of a funnel-tube ; the copper is immediately attacked and dissolved, forming cupric nitrate (Fig. 64), and at the same time nitric oxide gas is dis- engaged. This gas absorbs oxygen from the air and is con- FIG. 64. verted into red vapors, which are at first apparent in the gas- bottle, but as the evolution of nitric oxide continues, the gas in the flask gradually becomes colorless, and may then be col- lected in jars over water. Properties. Nitric oxide is a colorless gas. It has recently been liquefied by Cailletet. It is decomposable by heat, but less easily than the monoxide. It is scarcely soluble in water, which only takes up a twentieth of its volume. Its most charac- teristic property is the energy with which it absorbs half its volume of oxygen, passing into the state of nitrogen peroxide or red vapors, a* 154 ELEMENTS OF MODERN CHEMISTRY. If a jar filled with nitric oxide be opened to the air, the red vapors appear at once. 2NO -f O 2 = N 2 4 Nitric oxide supports the combustion of certain substances. Phosphorus burns in it brilliantly, but the gas does not, like oxygen and nitrogen monoxide, relight a taper still presenting a spark. Hydrogen decomposes nitric oxide at a temperature but slightly elevated, forming water and nitrogen. NO -f- H 2 = N -f H 2 The mixture of the two gases in equal volumes takes fire on the application of flame. If a few drops of carbon disulphide be poured into a jar of nitric oxide, the vapor of the volatile liquid is at once diffused throughout the gas, and on the approach of a lighted taper a brilliant flash of light is produced, the sulphur and carbon being burned by the oxygen of the nitric oxide. The light produced by this combustion determines at once, and like the solar light, the combination of chlorine and hydro- gen. When a mixture of nitric oxide with an excess of hydrogen is passed through a heated tube containing platinum sponge, water and ammonia are formed. NO -f 5H == H 2 -f NH 3 Under other circumstances hydroxylamine may be produced. A solution of ferrous sulphate absorbs nitric oxide with avidity, assuming a dark-brown color ; this is a characteristic property, by which nitric oxide may be recognized. NITROGEN TRIOXIDE. This compound is formed when a mixture of nitric oxide with a large excess of oxygen is subjected to intense cold. It is also formed, together with nitric acid, when nitrogen perox- ide is treated with a small quantity of cold water. 2N*O* -f H 2 O = 2HN0 3 -f N 2 3 Nitrogen peroxide. Nitric acid. It is a blue liquid, which boils at a low temperature. NITROGEN PEROXIDE. 155 NITROGEN PEROXIDE. NO 2 or N 2 0* Preparation. When well dried lead nitrate is heated to redness it is decomposed into lead oxide and nitrogen peroxide, which may be condensed in a well-cooled receiver. Pb(N0 3 ) 2 PbO Lead uitrate. Lead oxide. The first portions of nitrogen peroxide that are condensed generally retain a trace of moisture, and present a green color ; if the receiver be then changed, there collects a yellow liquid which solidifies to a crystalline mass at 10. Properties. Nitrogen peroxide is a mobile liquid, almost colorless at very low temperatures ; at it has a somewhat darker color, and at 15 it is orange-brown. It boils at 22, and its vapor is red. Near the point of ebullition its volu- metric composition corresponds to the formula N 2 0* ; that is, two volumes of nitrogen and four volumes of oxygen are con- densed into two volumes of N 2 4 , and occupy the same space as two atoms (one molecule) of hydrogen. But at a higher temperature this vapor is dissociated ; that is, it is gradually decomposed in such a manner as to occupy double its primitive volume. The two atoms of nitrogen and four atoms of oxygen which constitute two volumes of N 2 0* at a low temperature, occupy four volumes at about 70. NO 2 NO 2 NO 2 N|0 2 Red vapors at 20. Red viipors at 70. The vapor of nitrogen peroxide is very corrosive, and dan- gerous to inhale. A small quantity of cold water decomposes nitrogen perox- ide into nitrogen trioxide and nitric acid ; a larger quantity of water causes the formation of nitrous and nitric acids. N 2 4 H 2 = HNO 2 -f Nitrous acid. HNO 3 Nitric acid. 156 ELEMENTS OF MODERN CHEMISTRY. When a mixture of nitrogen peroxide and hydrogen is passed over heated platinum sponge, water and ammonia are formed. Nitryl Chloride and Bromide. Like nitric oxide, which may be called nitrosyl, nitrogen peroxide may play the part of a radical. There exists a chloride and also a bromide of nitro- gen peroxide or nitryl. N0 2 C1 N0 2 Br Nitryl chloride. Nitryl bromide. The latter compound is formed, together with other products, when bromine acts upon nitrogen peroxide at a very low tem- perature. The chloride of nitryl has recently been obtained by the reaction of phosphorus oxychloride upon silver nitrate. POCP -f 3AgN0 3 == Ag 3 PO* + 3(N0 2 C1) Phosphorus Silver nitrate. Silver phosphate. Nitryl chloride. oxychloride. Nitryl chloride is a light-yellow liquid, boiling at -|-5 and solidifying at 31. In contact with water, it forms nitryl hydrate (nitric acid), and hydrochloric acid. N0 2 C1 + H 2 = HC1 -j- HNO 3 In this reaction, the nitric acid is formed at the expense of the water, of which one atom of hydrogen is removed by the chlorine and replaced by the radical nitryl. Hence nitric acid and water may be said to belong to the same type : HOH (N0 2 )OH Water. Nitric acid. It is seen that in nitric acid the group NO 2 replaces one atom of hydrogen in water, this group is therefore monatomic. But the atom of hydrogen in nitric acid may also be replaced by another nitryl group, and the result is an oxide of nitryl, the anhydride of nitric acid, or nitrogen pentoxide. The fol- lowing formulae will illustrate the relations between these com- pounds and water which is their type : H lo N 2 lo N 2 H } C H | C NO 2 Water. Nitric acid. Nitrogen pentoxide. (Nitryl hydrate.) (Nitryl oxide.) NITROGEN PENTOXIDE NITRIC ACID. 15*7 NITROGEN PENTOXIDE. (NITRIC ANHYDRIDE.) This compound was obtained by H. Sainte-Claire Deville by the action of chlorine upon dry silver nitrate heated to between 58 and 60. 2AgN0 3 + CP = N'O 5 + 2AgCl + Silver nitrate. Nitrogen pentoxide. Silver chloride. It may also be obtained by passing the vapor of nitryl chlo- ride over silver nitrate heated to 70. AgO.NO 2 -f N0 2 C1 = AgCl + (N0 2 ) 2 0. Silver nitrate. Nitryl chloride. Nitrogen pentoxide. Also, as shown by Berthelot, by the action of phosphorus pentoxide upon concentrated nitric acid. 2HN0 3 H 2 N 2 5 Nitrogen pentoxide is solid and crystallizes in right-rhombic prisms. It melts at 29.5, and boils between 48 and 50. It is very unstable and explodes spontaneously even when it is preserved at a low temperature. NITRIC ACID. HNQ3 The atmosphere frequently contains a trace of nitric acid vapor or other compounds of nitrogen and oxygen, and small quantities of ammonium nitrate and nitrite may be detected in rain-water. After passing a current of air for a long time through a solution of potassium carbonate, the liquid is found to contain potassium nitrate (Cloez). It may be admitted that the compounds of nitrogen and oxygen are formed directly by the action of electricity upon the elements of the air. * The nitrates of potassium, sodium, magnesium, and calcium are met with in certain soils, often in abundance. They are formed wherever nitrogenized organic matters decompose in contact with the air and in presence of porous matters and alkaline bases. Under these circumstances, the ammonia re- sulting from the decomposition is oxidized to nitric acid. The experiments of Cloez have shown that the elements of 14 158 ELEMENTS OP MODERN CHEMISTRY. the air may unite directly, forming nitrates in the soil, wherever alkaline bases and oxidizable matters are present. Preparation. Nitric acid is obtained by decomposing an alkaline nitrate with sulphuric acid. In the laboratory, the operation may be conducted in a glass retort, the neck of which passes, without cork, into a cooled receiver. 98 parts of con- centrated sulphuric acid and 85 parts of sodium nitrate are employed. On the application of heat, nitric acid is vola- tilized, mixed at the commencement of the operation with red vapors. The acid condenses in the receiver as a yellow liquid, fuming in the air. Sodium acid sulphate remains in the retort. H 2 SO + NaNO 3 = g SO 4 -f- HNO 3 Sodium nitrate. Sodium acid sulphate. In the arts, the sodium nitrate is decomposed with a less concentrated sulphuric acid, the decomposition of the nitric acid during the operation being thus avoided. The operation is conducted in cast-iron retorts, A (Fig. 65), the lateral tubes of which, B, are adapted to stoneware tubes communicating Fio. 65. with a series of stoneware bottles, D, where the acid con- denses. The temperature is elevated towards the close of the operation, and sodium neutral sulphate is formed. H 2 SO* -f 2NaN0 3 = Na 2 S0 4 -f 2HN0 3 NITRIC ACID. 159 Properties. When perfectly pure, nitric acid is colorless, but it rapidly becomes yellow under the influence of light, undergoing a partial decomposition. When exposed to the air, it gives off abundant white fumes. Its density is 1.52 ; it solidifies at 49, and boils at 86. When its vapor is passed through a red-hot porcelain tube, it is decomposed into nitrogen peroxide, oxygen, and water. 2HN0 3 H 2 + N 2 4 + The mixture of nitric acid with water produces an elevation of temperature. The dilute acid, formed by mixing 42.8 parts of water and 100 parts of the concentrated acid, is a colorless liquid, boiling constantly at 123 ; yet it cannot be considered as a definite compound (Roscoe). Nitric acid readily gives up a portion of its oxygen to bodies having an affinity for that element. It energetically oxidizes sulphur, phosphorus, arsenic, iodine, silicon, carbon, and most of the metals. If nitric acid be poured upon red-hot charcoal, the combus- tion is vividly intensified by the decomposition of the nitric acid, and red fumes appear at the same time. Copper decomposes nitric acid with an abundant disengage- ment of nitric oxide, which is converted into nitrogen peroxide by contact with the air. Certain metals attack the dilute acid more readily than the concentrated ; iron is one of these metals. If dilute nitric acid be poured upon clean iron wire, chemi- cal action at once takes place, and there is an abundant evolu- tion of red vapor ; but if the same wire be plunged into the concentrated acid, no action is manifested ; and further, if the strong acid be poured off and replaced by dilute acid, the latter undergoes no decomposition ; the iron has become passive by becoming covered with a thin layer of gas. But if its surface be touched with a copper wire, chemical action is at once re- established between the iron and the nitric acid. The action of tin upon nitric acid is worthy of notice. Tor- rents of red vapor are disengaged, and the metal is converted into a white powder, which is stannic acid. In this reaction small quantities of ammonia and hydroxylamine are formed at the expense of the elements of the nitric acid, and remain combined with the excess of acid. The conversion of nitric acid into ammonia may be more 160 ELEMENTS OP MODERN CHEMISTRY. complete. If zinc be introduced into very dilute nitric acid, the metal dissolves slowly and without disengagement of gas ; the liquid is then found to contain zinc nitrate and ammo- nium nitrate. The nascent hydrogen set free from a portion of the nitric acid by the zinc reduces another portion of the acid, forming water and ammonia. Zn -f 2HN0 3 = Zn(N0 3 ) 2 + H 2 Zinc. Zinc nitrate. 2HN0 3 + 4H 2 = 3H 2 + (NH 4 )N0 3 Ammonium nitrate. Nitrogen dioxide decomposes nitric acid. When a current of this gas is passed through nitric acid, the latter becomes colored, according to its concentration, brown, yellow, or bluish- green. Under these circumstances the acid is reduced, and either nitrogen peroxide or nitrous acid is formed and remains dissolved in the liquid, the former communicating a brown, the second a blue or green color. Nitric acid is one of the most important acids ; it is largely used as a reagent. It is employed in the manufacture of sul- phuric acid, and also to oxidize certain organic matters, such as starch and sugar, which it converts into oxalic acid. Nitro-hydrochloric Acid. A mixture of nitric and hydro- chloric acids is called nitro-hydrochloric or nitro-muriatic acid, or aqua regise. This liquid dissolves gold and platinum, and it owes this property to the chlorine, which is set at liberty by the mutual action of the two acids. 2HC1 + 2HN0 3 = 2H 2 -f N 2 4 + Cl 2 When the mixture is left to itself it gradually assumes a yellow color, undergoing a partial decomposition, as indicated by the above formula ; but this decomposition is limited, and only complete in the presence of a metal capable of absorbing the chlorine. But the reaction between hydrochloric and nitric acids gives rise to the formation of other products, noticed by Gay-Lussac and Baudrimont ; these are ternary compounds of oxygen, ni- trogen, and chlorine. One is a red vapor, condensing at 7 to an orange-red liquid. Its composition is probably expressed by the formula NOC1 2 . It may be regarded as nitrogen peroxide in which one atom of oxygen is replaced by an equivalent quantity, that is, two atoms, of chlorine. PHOSPHORUS. 161 The other is a gas which does not liquefy at very low tem- peratures ; it is nitrosyl chloride, NO.C1. By reacting' with water it forms hydrochloric and nitrous acids. NO.C1 + H 2 = HC1 + NO.OH It will be noticed that nitrosyl chloride bears the same rela- tion to nitrous acid that nitryl chloride bears to nitric acid. The following formulae will illustrate the constitution of these bodies : Nori N0 lo N0 lo H { L NO } L Nitrcteji chloride. Nitrous acid. Nitrogen trioxide. NO'Cl N 2 lo N 2 H j L NO 2 Nitryl chloride. Nitric acid. Nitrogen pentoxide. PHOSPHORUS Vapor density compared to air 4.32 Vapor density compared to hydrogen .... 61.1 Atomic weight P =31. Brandt, an alchemist of Hamburg, while attempting to ex- tract the philosopher's stone from urine, discovered phosphorus in 1669. But urine contains only a small quantity of phos- phates and can yield but traces of phosphorus, so that this body only became generally known to chemists after Gahn demonstrated its existence in bones, and Scheele discovered the process for its extraction. The process of the latter chemist is still in use ; it consists in treating bone-ash with dilute sulphuric acid, by which means the tricalcium phosphate of the bones is converted into mono- calcium phosphate, ordinarily called acid phosphate of lime. Ca 3 (P0 4 ) 2 + 2H 2 SO = CaH 4 (P0 4 ) 2 + 2CaSO* Tricalcinm Calcium acid Calcium phosphate. phosphate. sulphate. The latter phosphate being soluble is separated from the calcium sulphate by filtration, and the solution is evaporated and mixed with powdered charcoal. The mixture is dried and gradually heated to redness in cast-iron vessels. By this means the calcium acid phosphate is converted into calcium meta- phosphate by the expulsion of two molecules of water. CalP(PO) 2 = 2H 2 + Ca(P0 3 ) 2 Calcium acid phosphate. Calcium metaphosphate. 162 ELEMENTS OP MODERN CHEMISTRY. The latter is strongly heated with charcoal in clay retorts (Fig. 66), and is decomposed, yielding carbon monoxide and phosphorus which distils over, and leaving a residue of calcium pyrophosphate. 2Ca(P0 3 ) 2 Calcium metaphosplmte. + 50 = Ca 2 P 2 7 Calcium pyrcphosphate. 5CO + Carbon monoxide. p'2 The phosphorus condenses in the water in the receiver A, in which the neck of the retort C is engaged. FIG. 66. As it is impossible to expel all of the water from the calcium acid phosphate, this water is decomposed by the charcoal, hy- drogen and carbon monoxide being formed, together with a small quantity of phosphoretted hydrogen. 100 kilogrammes of bone yield between 8 and 9 kilo- grammes of phosphorus. The latter is purified by enclosing it in a chamois-skin sack, and strongly compressing it under water at 50 ; the phosphorus passes through the leather and collects under the water. It is moulded into sticks by being drawn up into slightly conical glass tubes, which are then plunged into cold water. The phosphorus solidifies and is easily drawn from the tubes. Physical Properties. Recently-fused phosphorus is trans- parent, colorless, or having a pale-yellow tint, flexible, and soft PHOSPHORUS. 163 enough to be easily scratched by the nail. One-tenth per cent, of sulphur renders it hard and brittle. It has a well-marked odor, slightly resembling that of garlic. Its density at 10 is 1.83. It melts at 44 and boils at 290 ; its vapor is colorless and has a density of 4.32 compared to air, or 61.1 compared to hydrogen. If one volume of hydrogen weighs 1, one volume of vapor of phosphorus weighs 61.1, and this number should represent the weight of one atom of phosphorus ; now it represents the weight of two atoms, and the vapor of phosphorus presents the singular anomaly that it contains in the same volume twice as many atoms as the simple gases, such as hydrogen or nitrogen. If one volume of hydrogen contain one atom, one volume of phosphorus vapor contains two, and heat cannot dissociate these two atoms in such a manner that they may occupy two volumes instead of one. The vapor of arsenic presents the same anomaly. II P 2 As 2 1 volume of 1 volume of 1 volume of 1 volume of hydrogen. nitrogen. phosphorus vapor. arsenic vapor. Phosphorus volatilizes below its boiling-point and even below its melting-point. At ordinary temperatures it emits vapors in a vacuum and even in the air. It is luminous in the dark, from which property it derives its name, which signifies light- bearer. The cause of this phenomenon is still obscure, but is generally attributed to the slow oxidation which phosphorus undergoes in the air. When a stick of transparent phosphorus is kept under water, it gradually becomes opaque and covered with a yellowish-white pulverulent powder, while the central parts retain their trans- parence. This white phosphorus is still pure, but the surface of the stick has divided into a multitude of little particles which present a crystalline appearance. Some of them become de- tached and remain suspended in the water, giving to the latter the property of being luminous in the dark. Phosphorus is rapidly dissolved by carbon disulphide and is deposited in rhombic dodecahedra on the slow evaporation of the solution. There is an amorphous variety of phosphorus which differs so much from ordinary phosphorus that it presents the prop- 164 ELEMENTS OF MODERN CHEMISTRY. erties of an entirely different substance. It has a dark brown- red color, and is not luminous in the dark. It is insoluble in carbon disulphide ; it does not melt and take fire like ordi- nary phosphorus when heated to 50. It is amorphous, and presents a conchoidal fracture. Its density is 2.14. Ordinary phosphorus is one of the most dangerous poisons, but this red body exerts no action upon the economy. At 260 amor- phous phosphorus melts, is converted into ordinary phospho- rus, and presents the properties of the latter substance on cooling. Amorphous phosphorus results from a physical change brought about by the action of light or heat on the ordinary variety. If a stick of phosphorus be exposed to direct sun- light, its surface assumes a red color ; or if it be maintained for a long time at a temperature of 240, it is entirely con- verted into the amorphous variety. This transformation is also accomplished by the influence of certain chemical agents. If a small stick of ordinary phos- phorus be introduced into a test-tube and a very minute por- tion of iodine be allowed to fall upon it, the iodine unites with the phosphorus with the production of light and heat. A trace of phosphorus iodide is formed, and the remainder of the phos- phorus is converted into a hard, black mass, which yields a red powder ; this is amorphous phosphorus (E. Kopp, Brodie). Thus prepared, this body volatilizes like arsenic, without melting, and can be distilled without alteration, condensing in a black mass, which contains only traces of iodine. Chemical Properties, Ordinary phosphorus possesses a strong affinity for oxygen. When exposed to the air it slowly oxidizes, and the slow combustion, aided by the moisture of the air, produces a mixture of phosphorous and phosphoric acids. Schbnbein has shown that the slow oxidation of phosphorus is accompanied by the formation of small quantities of ozone and hydrogen dioxide, and he asserts that ammonium nitrite is formed at the same time. When heated in the air to a temperature of 60, phosphorus takes fire and burns, producing a bright light and white vapors of phosphorus pentoxide. In pure oxygen the combustion is accomplished with great brilliancy. Phosphorus may be burned under warm water by passing a current of oxygen through the melted element by means of a tube drawn out to a point (Fig. 67); each bubble of oxygen HYDROGEN PHOSPHIDE. 165 which comes in contact with the phosphorus produces a bright flash. Phosphorus takes fire spontaneously in an. atmosphere of dry chlorine, phosphorus pentachloride being produced. Uses of Phosphorus. This body is principally employed in the manufacture of matches. The inflammable tips of friction- matches contain either ordinary or amorphous phosphorus. In the first case, the phosphorus is mixed with inert substances, such as sand or ochre, held together by strong glue ; in the - FIG. 67. second case, the ignition of the amorphous phosphorus, which is but slightly combustible, is determined by potassium chlorate, to which is also added antimony sulphide. All of these sub- stances are made into a paste, into which the ends of the matches are dipped. Sometimes the match-sticks are tipped with a paste composed of potassium chlorate and antimony sulphide, a mixture which only takes fire by friction upon a prepared surface, composed generally of amorphous phosphorus and antimony sulphide. All of these mixtures are held to- gether by strong glue. HYDROGEN PHOSPHIDE. Density compared to air 1.134 Density compared to hydrogen 17. Molecular weight PH 3 = 34. This gas was discovered by Gengembre in 1*783. When phosphorus is heated with a solution of caustic potassa, there is a gas disengaged, which inflames spontaneously on con- tact with the air ; this is hydrogen phosphide. It is formed according to the following equation : 3KOH + 4P + 3H 2 = 3KH 2 P0 2 + PH 3 Potassium hydrate. Potassium hypophoephite. 166 ELEMENTS OF MODERN CHEMISTRY. Preparation. 1. Hydrogen phosphide may be prepared by heating phosphorus with a strong solution of potassium hydrate, or with thick miljc of lime, with which the flask (Fig. 68) FIG. 68. should be almost entirely filled. The gas is conducted under the surface of water, and as each bubble arrives in contact with the air it takes fire spontaneously, producing a bright flash and a wreath of white smoke, which enlarges as it rises in the air. 2. The same spontaneously inflammable gas is evolved when calcium phosphide is thrown into water (Fig. 69). The phos- phide of calcium is prepared by passing vapor of phosphorus over fragments of incandescent lime ; it instantly decomposes water with formation of calcium hypophosphite and sponta- neously inflammable hydrogen phosphide. However, when calcium phosphide is treated with hydro- chloric acid, hydrogen phosphide is produced, which does not take fire without the application of heat (Fig. 70). In this case, the gas is formed by double decomposition between the hydrochloric acid and the calcium phosphide ; the calcium combines with the chlorine, forming calcium chloride, and the hydrogen of the acid combines with the phosphorus. 3. In the same manner, when phosphorous acid is strongly heated in a small retort, it evolves a hydrogen phosphide which is not spontaneously inflammable. 4H 3 P0 3 = PH 3 + 3H 8 PO* Phosphorous acid. Phosphoric acid. COMPOUNDS OF PHOSPHORUS AND CHLORINE. 167 Properties, The gas thus obtained is colorless, and pos- sesses a garlicky odor. It is but slightly soluble in water, but is soluble in alcohol and in ether. When it is pure it does not take fire in the air at a temperature below 100, and then burns with a very luminous white flame. According to Paul Thenard, the spontaneous inflammability of the hydrogen phos- phide prepared by the methods first mentioned is due to the FIG. 69. FIG. 70. presence of another phosphide, P' 2 H 4 ; this is a very volatile liquid, extremely inflammable, and the least trace of its vapor in hydrogen phosphide gas communicates to the latter the property of spontaneous inflammability. Hydrogen phosphide is absorbed by a solution of cuprie sulphate, with the formation of black phosphide of copper. The composition of hydrogen phosphide, PH 3 , recalls that of ammonia, NH 3 , and the analogy between the two gases is further revealed by the property common to both of uniting with hydriodic acid. There is a compound of hydrogen phos- phide with hydriodic acid, a well-defined, solid body, crystal- lizing in brilliant cubes. PII'.HI or PH 4 I phosphonium iodide. The existence of a solid phosphide of hydrogen has been demonstrated, and the formula P 2 H attributed to it. COMPOUNDS OF PHOSPHORUS AND CHLORINE. There are two chlorides of phosphorus : Phosphorus trichloride PCI 3 Phosphorus pentachloride PCI 4 168 ELEMENTS OF MODERN CHEMISTRY. There are, besides, Phosphorus oxychloride POC1 3 Phosphorus sulphochloride PSC1 3 PHOSPHORUS TRICHLORIDE. PC1 When a current of dry chlorine is passed over phosphorus heated in a small tubulated retort, a liquid compound of chlo- rine and phosphorus is formed and may be condensed in a cooled receiver. This is phosphorus trichloride. It is a fuming, colorless liquid, having a density of 1.45 and boiling at 74. If it be poured into water, it at first sinks to the bottom, and then rapidly disappears, evolving white fumes of hydro- chloric acid, and forming phosphorous acid, which remains in solution. POP + 3H 2 = H 3 P0 3 + 3HC1 PHOSPHORUS PENTACHLORIDE. PCI* In contact with an excess of chlorine, phosphorus trichloride absorbs two more atoms of that gas, and condenses into a yellow crystalline solid, phosphorus pentachloride. This body is volatile, and sublimes without fusion when heated, even below 100. When heated under pressure, it melts at 148 and boils at a slightly higher temperature. Its vapor density, taken at 336 and reduced to 0, is equal to 3.656. This density should be double, supposing that the molecule PCI 5 occupies two volumes. The anomaly, however, is only apparent, for there are good reasons for believing that at the temperature 336 the vapor of phosphorus pentachloride no longer exists, and that the compound is decomposed or dis- sociated into a mixture of phosphorus trichloride and chlorine, a mixture which would give four volumes of vapor for one molecule of PCI 5 . _ f PCI 3 = 2 volumes. : { Cl 2 = 2 volumes. 4 volumes. Indeed, when the vapor density of phosphorus pentachloride is taken by diffusing it in the vapor of the protochloride, which PHOSPHORUS OXYCHLORIDE. 169 prevents the dissociation before mentioned, a figure is found which corresponds very nearly with the theoretic density 7.21 (A. Wurtz). Phosphorus pentachloride decomposes water with energy, forming hydrochloric and phosphoric acids. PCI 5 + 4H 2 = H 3 PO + 5HC1 When only a small quantity of water is present, hydrochloric acid is disengaged, by the exchange of two atoms of chlorine for one atom of oxygen, and a colorless liquid is formed which is called phosphorus oxychloride. When heated in a current of hydrogen sulphide, phosphorus pentachloride is converted into the sulphochloride, a colorless liquid boiling at 126. PCI 5 + H 2 == 2HC1 + POCP PCI 5 4- H 2 S = 2HC1 4- PSCP PHOSPHORUS OXYCHLORIDE. POCP This body is readily obtained by exposing phosphorus penta- chloride to moist air until it becomes liquid, and subsequently distilling the liquid (A. Wurtz). It is formed in a great num- ber of reactions when phosphorus pentachloride is heated with hydrated acids, such as oxalic acid, boric acid, etc., or with oxides, such as phosphoric oxide. In these cases, one atom of oxygen from the oxidized body is exchanged for two atoms of chlorine from the pentachloride (Gerhardt). Phosphorus oxychloride is a colorless liquid, boiling at 110. When poured into water, it sinks and is at once decomposed, hydrochloric and phosphoric acids being formed. POCP + H* 3 = ' + 3HC1 Phosphorus oxychloride. 3 molecules water. Phosphoric acid. COMPOUNDS OF PHOSPHORUS WITH BROMINE AND IODINE. Two bromides of phosphorus are known : Phosphorus tribromide, PBr 3 , a colorless liquid. Phosphorus pentabromide, PBr 5 , a yellow, crystalline mass. To the trichloride and tribromide of phosphorus there cor- responds a triiodide, concerning which but little is known. H 15 1*70 ELEMENTS OF MODERN CHEMISTRY. The best defined and most important combination of phos- phorus with iodine is the compound P 2 I*. Phosphorus Iodide, P 2 I*. This body is obtained by dis- solving 26 parts of dry phosphorus in 30 or 40 times its weight of carbon disulphide, and gradually adding to the solution 203.4 parts of iodine. The liquor, at first reddish-yellow, becomes orange-yellow ; it is distilled on the water-bath to drive out a part of the carbon disulphide, and on cooling it deposits a bright-red, crystalline mass. This is the iodide P 2 I*. It crystallizes in long, brilliant, flattened needles, which are flexible, and melt at 100. On contact with water it is decom- posed, forming phosphorous and hydriodic acids, and at the same time depositing a yellow, flocculent precipitate rich in phosphorus (Corenwinder). COMPOUNDS OF PHOSPHORUS AND OXYGEN. Phosphorus combines with oxygen, forming two oxides : Phosphorus trioxide, or phosphorous oxide . . P 2 3 Phosphorus pentoxide, or phosphoric oxide . . P 2 5 Each of these oxides can combine with three molecules of water, phosphorous and phosphoric acids being thus formed. P 2 3 -f 3H 2 = 2H 3 P0 3 P 2 5 -f 3H 2 == 2H 3 P0 4 Besides these two acids there is another containing less oxy- gen ; it is hypophosphorous acid, whose corresponding oxide is unknown. These three acids form a series containing for three atoms of hydrogen and one atom of phosphorus regularly-in- creasing quantities of oxygen ; they may be said to constitute different degrees of oxidation of hydrogen phosphide. PH 3 hydrogen phosphide. PH 3 (missing). PH 3 2 hypophosphorous acid. PH 3 3 phosphorous acid. PH 3 4 phosphoric acid. Constitution -of the Oxygen Acids of Phosphorus. Phos- phorous and phosphoric acids are related, the first to phos- phorus trichloride, the second to phosphorus oxychloride. In HYPOPHOSPHOROUS ACID. 171 fact, they are derived from these compounds by the action of water. P'"CP phosphorus trichloride. P(OH) 3 phosphorous acid (phosphorus trihydrate). (PO)'"C1 3 phosphorus oxychloride (phosphoryl trichloride). (PO)'"(OH) 3 phosphoric acid (phosphoryl trihydrate). To phosphorus pentachloride, PCI 5 , would correspond a pen- tahydrate, P(OH ) 5 , which is unknown. Phosphoric acid would be derived from the latter by the loss of a molecule of water. P(OH) 5 = H 2 + (PO)(OH) 3 It is seen that in phosphorous acid, as in the trichloride, phos- phorus is regarded as playing the part of a triatomic element, while it is pentatomic in the pentachloride. In hypophosphorous acid, it must be admitted that one atom of hydrogen is united directly to the triatomic phosphorus, and its constitution is expressed by the formula H OH OH HYPOPHOSPHOROUS ACID. H'PO 2 When phosphorus is boiled with milk of lime or with a con- centrated solution of baryta, a soluble hypophosphite is pro- duced, and on treating the solution of barium hypophosphite with sulphuric acid, a precipitate of barium sulphate and a solution of hypophosphorous acid are obtained ; they may be separated by filtration. When sufficiently concentrated, the liquor leaves a colorless and very acid syrupy residue, which constitutes hypophosphorous acid. This acid is decomposed at a high temperature, yielding phosphoric acid and hydrogen phosphide. It is gifted with energetic reducing properties : it instantly decomposes the salts of mercury and silver, setting free the metal. An excess of hypophosphorous acid added to a solution of cupric sulphate precipitates, by the aid of a gentle heat, hydride of copper, Cu 2 H 2 , which is decomposed at 100 into copper and hydrogen (A. Wurtz). 172 ELEMENTS OF MODERN CHEMISTRY. Hypophosphorous acid contains three atoms of hydrogen, only one of which is capable of being replaced by an equiva- lent quantity of a metal. The composition of the hypophos- phites is consequently expressed by the following general formula : R'H'PO* in which B/ represents a monatomic metal, such as potassium, capable of replacing hydrogen atom for atom. PHOSPHOROUS ACID. H3PQ3 Preparation. Phosphorous acid results from the action of water upon phosphorus trichloride, as already seen. It may be obtained in a state of purity by evaporating the acid liquor resulting from this reaction, and heating the syrupy residue in a platinum capsule until the odor of hydrogen phosphide is perceptible. On cooling, the acid solidifies to a crystalline mass. Properties. These crystals absorb moisture when exposed to the air, and are resolved into an intensely acid liquid ; they melt at a gentle heat, and are decomposed by a high tempera- ture into hydrogen phosphide and phosphoric acid. Like hypophosphorous acid, phosphorous acid possesses re- ducing properties. Its boiling aqueous solution reduces the salts of mercury, silver, and gold, and this reduction is favored by the presence of ammonia. It converts arsenic acid into arsenious acid. Chlorine, bromine, and iodine convert it into phosphoric acid in presence of water. H 3 P0 3 + H 2 O + Cl 2 = 2HC1 + H 3 PO* Phosphorous acid contains three atoms of hydrogen, two of which are replaceable by an equivalent quantity of a metal. It is hence called a dibasic acid. The composition of the neutral hypophosphites is expressed by the general formula ITHPO 3 , in which R' represents a monatomic metal like potassium or sodium. PHOSPHORIC OXIDE PHOSPHORIC ACID. 173 PHOSPHORIC OXIDE, OR PHOSPHORUS PENTOXIDE. (PHOSPHORIC ANHYDRIDE.) This compound may be obtained by burning phosphorus in a large globe filled with dry air. A dense white smoke is pro- duced, and condenses upon the walls of the vessel in flakes like snow. This body is the anhydride of phosphoric acid. When exposed to the air, it absorbs moisture and is converted into metaphosphoric acid. _ H 2 = 2HP0 3 When thrown into water it dissolves with a hissing noise, such as is produced by a red-hot iron. Phosphoric acid volatilizes at a dull-red heat ; it is undecom- posable by heat. It yields the oxychloride when distilled with phosphorus pentachloride. P 2 5 + 3PC1 5 = 5POC1 3 It also yields phosphorus oxychloride when distilled with dry common salt (Lautemann). PHOSPHORIC ACID. (ORTHOPHOSPHORIC ACID.) H'PO* Preparation. 1. This acid may be prepared by boiling phosphorus with nitric acid. On account of the violence of the reaction the operation is difficult to regulate, and even dangerous when ordinary phosphorus is employed, but it succeeds very well with powdered amorphous phosphorus. This is heated with tolerably concentrated nitric acid in a retort, fitted with a receiver, and, when the whole of the phos- phorus has disappeared, a little nitric acid is added to the contents of the retort, and the liquid is concentrated in a platinum capsule. When the last portions of nitric acid have been driven out, a small quantity of water is added, and the syrupy liquid is placed in a bell-jar over a dish containing concentrated sulphuric acid. At the end of some time, the 15* 174 ELEMENTS OF MODERN CHEMISTRY. phosphoric acid is deposited in the form of hard, transparent, prismatic crystals. 2. A current of chlorine may be passed through warm water under which is a layer of melted phosphorus. Phosphoric acid and hydrochloric acid are formed. PCI 5 + 4H 2 = H 3 PO 4 -f 5HC1 As soon as all of the phosphorus has disappeared the solution is evaporated, and the hydrochloric acid is driven out by heating the residue to 200. The residue is dissolved in water and forms a solution which will deposit the acid in crystals when concentrated as indicated above. Properties. When exposed to the air, these crystals attract moisture and deliquesce. Their solution is very acid. It does not coagulate white of egg, and it produces no cloud in a solu- tion of barium chloride, but it forms a white precipitate of ammonio-magnesium phosphate in a solution of magnesium sulphate on the addition of ammonia. With silver nitrate to which ammonia has been added, it gives a yellow precipitate of trisilver phosphate, Ag 3 PO*. Orthophosphoric acid contains three atoms of hydrogen, each of which is replaceable by an equivalent quantity of metal. PYROPHOSPHORIC ACID. When orthophosphoric acid is heated for a long time to 213 it loses water and is converted into a new acid, which is called pyrophosphoric. Two molecules of phosphoric acid lose one molecule of water, and then unite to form a single mole- cule of pyrophosphoric acid. /OH PO^-OH /OH \^ TT PO vOH = H 2 PO OH PO^-OH X OH The residue constitutes an opaque, semi-crystalline mass, composed almost entirely of pyrophosphoric acid. METAPHOSPHORIC ACID. 175 Its aqueous solution forms a white precipitate of silver pyrophosphate in solutions of silver nitrate. H*P 2 7 .+ 4AgN0 3 == Ag 4 P 2 7 + 4HN0 3 When heated with water, pyrophosphoric acid again com- bines with one molecule of that liquid, and is converted into phosphoric acid by a reaction the inverse of that by which it is formed. METAPHOSPHORIC ACID. HFC* Preparation. When phosphoric acid is heated to redness in a platinum crucible, a hard, transparent, vitreous mass is obtained on cooling ; this is metaphosphoric acid. It is formed by the abstraction of one molecule of water from phosphoric acid. H 3 PO* H 2 = HPO 3 It may also be obtained directly from calcium acid phos- phate, the preparation of which from bone-ash has already been described. A slight excess of dilute sulphuric acid is added to the concentrated solution of this salt, and the insoluble cal- cium sulphate formed is separated by nitration. Since, how- ever, the calcium sulphate is not entirely insoluble in water, the solution is concentrated, and alcohol added, which com- pletely precipitates the sulphate. The liquid is again filtered, the alcohol driven off by evaporation, and the residue heated to a temperature near redness to remove the excess of sulphuric acid. On cooling, a vitreous mass of metaphosphoric acid is ob- tained. An aqueous solution of metaphosphoric acid instantly pro- duces a precipitate of silver metaphosphate in a solution of silver nitrate. HPO 3 + AgNO 3 === AgPO 3 -f HNO 3 A few drops of the acid solution added to white of egg sus- pended in water produces an abundant white precipitate. The same metaphosphoric acid is formed when phosphoric oxide is thrown into a large quantity of cold water, or when it is allowed to deliquesce in the air. Under these circumstances, 176 ELEMENTS OF MODERN CHEMISTRY. one molecule of phosphoric oxide combines with only one molecule of water. P 2 5 4- IPO = 2HP0 3 The preceding considerations establish the existence of three phosphoric acids, which differ both in composition and proper- ties. To these three acids correspond three salts of silver, and it will be seen that the latter differ from the acids only by containing silver instead of hydrogen, a substitution which takes place atom for atom. ACIDS. SILVER SALTS. H 3 PO* phosphoric acid (orthophos- Ag 3 P0 4 trisilver phosphate (ortho- phoric). phosphate). H 4 P 2 7 pyrophosphoric acid. Ag 4 P 2 7 silver pyrophosphate. HPO 3 inetaphosphoric acid. AgPO 3 silver inetaphosphate. It may be added that, independently of the acids and salts of which the composition and nomenclature have just been considered, others have been described, the most interesting of which are related to the metaphosphates, of which they con- stitute polymeric modifications. That is, two, three, four, or more molecules of metaphosphoric acid are condensed in a single molecule, forming more complicated acids. COMPOUNDS OF PHOSPHORUS AND SULPHUR. When phosphorus is heated with dry sulphur, or when a mixture of the two bodies is melted under water, they combine with a vivid combustion which is sometimes accompanied by dangerous explosions. The action is less violent with amor- phous phosphorus. According to the proportions of these bodies which are brought into contact, several combinations of phosphorus and sulphur may be obtained, among which the trisulphide, P 2 S 3 , and the pentasulphide, P 2 S 5 , correspond to phosphorous and phosphoric oxides. The pentasulphide may be obtained in pale yellow crystals. ARSENIC. Vapor density compared to air 10.37 Vapor density compared to hydrogen .... 150. Atomic weight As = 75. Arsenic was discovered by A. Schroeder in 1694. Natural State and Extraction. There exists in nature a ARSENIC. 177 common and abundant mineral which contains iron, sulphur, and arsenic, and which is called mispickel ; it is a sulphar- senide of iron. When it is strongly heated, the arsenic is volatilized and a residue of iron sulphide remains. FeSAs = FeS + As Mispickel. Iron sulphide. The operation is conducted on the large scale in earthenware cylinders placed horizontally in a furnace. The arsenic sublimes into sheet-iron pipes fitted to the open extremity of the cylin- ders which extend beyond the furnace. The volatilization of the arsenic is facilitated by the addition of a certain quantity of metallic iron. The arsenic of commerce may be purified by distilling it with charcoal in a stoneware retort. Properties. Recently-sublimed arsenic presents the appear- ance of a steel-gray, crystalline mass, having a metallic lustre. Its crystalline form is an acute rhombohedron. Its density is about 5.7. Arsenic volatilizes without melting at a temperature below dull redness. Its vapor is colorless. When it is heated under strong pressure it melts to a transparent liquid. On exposure to the air it loses its lustre and assumes a black-gray color ; in this case its surface becomes covered with a thin layer of a brown-black pulverulent substance, regarded by some chemists as a suboxide of arsenic. Arsenic oxidizes when it is heated in the air or in oxygen. If a small quantity of arsenic be thrown upon a red-hot coal, white vapors are produced, and an alliaceous odor is percep- tible. A fragment of arsenic may be strongly heated in the hori- zontal branch of a tube con- taining oxygen (Fig. 71) ; the metal takes fire and burns with bluish flame, producing white vapors of arsenious oxide. If arsenic be preserved from the air under a layer of water, in which it is insoluble, it oxidizes slowly, in such a manner as to form a small quantity of arsenious acid, which dissolves in 178 ELEMENTS OF MODERN CHEMISTRY. the water. This property explains the efficacy of powdered arsenic (commercial cobalt) for poisoning flies. If powdered arsenic be sprinkled into dry chlorine, each particle burns with a bright flash. The combustion indicates the energy of the combination. The arsenic unites with the chlorine, being converted into the trichloride AsCP. It also combines directly with bromine, with iodine, and with sulphur. HYDROGEN ARSENIDE, OR ARSENIURETTED HYDROGEN. Density compared to hydrogen 39. Molecular weight AsH 3 =78. Preparation. This gas may be prepared by the action of hydrochloric acid upon zinc arsenide. Zn 3 As 2 -f 6HC1 = 2AsH 3 + 3ZnCP Zinc arsenide. Zinc chloride. It is a gas which must be handled with great prudence, as it is extremely poisonous. Properties. Hydrogen arsenide is colorless; its odor is penetrating and garlicky. At a red heat it is decomposed into arsenic and hydrogen. On the application of flame, it burns in the air with a bluish light, producing fumes of arsenious oxide. If the supply of air be insufficient, arsenic is deposited. With one and a half times its volume of oxygen, hydrogen arsenide forms an explosive mixture, the products of the combination being water and arsenious oxide. 2AsH 3 -f O 6 = As 2 3 + 3H 2 Chlorine decomposes hydrogen arsenide with a production of light and the formation of hydrochloric acid. If an excess of chlorine be present arsenic trichloride is formed, but if the experiment be made in the presence of water, it is arsenious oxide which is formed. 2AsH 3 -{- 6C1 2 + 3EPO = As 2 3 -f 12HC1 Water dissolves about one-fifth of its volume of hydrogen arsenide. When this gas is agitated with a solution of cupric sulphate, it disappears entirely if the gas be pure, and leaves a residue of hydrogen should that gas have been present in the free state in the mixture (Dumas). SCuSO 4 -I- 2AsH 3 = Cu 3 As 2 -f 3H 2 SO* Cupric sulphate. Copper arsenide. ARSENIC CHLORIDE. ARSENIC-US OXIDE. 1*79 ARSENIC CHLORIDE. AsCl 3 Preparation. 1. A current of dry chlorine may be parsed over powdered arsenic contained in a retort, the neck of which is fitted to a cooled receiver. The chloride formed condenses as a yellow liquid, containing an excess of chlorine, from which it may be freed by distillation over powdered arsenic (Dumas). 2. A mixture of 40 grammes of arsenious oxide and 400 grammes of sulphuric acid is gently heated in a tubulated retort, and fragments of fused sodium chloride are gradually added; arsenic chloride distils over and condenses in the receiver. 3H 2 SO -f GNaCl + As 2 3 = 3Na 2 SO -f 2AsCl 3 + 3H 2 Sodium chloride. Sodium sulphate. Properties. Arsenic chloride is a colorless, oily, and very dense liquid. It boils at 134. Its density at is 2.05. It gives off white fumes in the air, and is very poisonous. An excess of water instantly decomposes it into hydrochloric acid and arsenious oxide, which, being but slightly soluble, is precipitated. 2AsCl 3 -|- 3H 2 = As 2 3 + 6HCI ARSENIOUS OXIDE. Preparation. This dangerous poison is obtained in the arts by roasting arseniferous minerals, particularly mispickel. Roasting is an operation which consists in heating a mineral in contact with air, by which the oxidizable elements present are oxidized. When arseniferous minerals are roasted, arsen- ious oxide is formed among other products, and volatilizes, and is condensed either in wide horizontal chimneys or in a large building divided into numerous communicating compartments, through which the vapor is led consecutively. It is collected in the form of a powder, and is resublimed in cast-iron pots surmounted by sheet-iron cylinders, in which it condenses. Properties. Recently-sublimed arsenious oxide occurs as vitreous masses ; but it soon loses its transparency and becomes milk-white, presenting the appearance of porcelain. When a large piece of the opaque oxide is broken, the interior is usually found to be still transparent and vitreous. 180 ELEMENTS OF MODERN CHEMISTRY. Arsenious oxide then exists in two forms : the vitreous variety is amorphous ; the opaque is crystalline. The former variety changes into the latter by a molecular transformation which takes place in the midst of the amorphous vitreous mass. Arsenious oxide crystallizes in regular octahedra or in tetra- hedra ; sometimes, but more rarely, in right-rhombic prisms. It is dimorphous. It dissolves slowly in cold water, in which it is but slightly soluble, and in this respect there is a curious difference between the opaque and the vitreous varieties. The latter is three times more soluble than the former ; while one part of the vitreous oxide dissolves in 25 parts of water at 13, one part of the opaque variety requires 80 parts of water for its solution at the same temperature. The aqueous solution of arsenious oxide feebly reddens blue litmus. It is almost tasteless. It may be regarded as contain- ing normal arsenious acid, H 3 As0 3 , corresponding to normal phosphorous acid, H 3 P0 3 ; but this hydrate cannot be separated from the solution. On evaporation, the oxide As 2 3 is always deposited. 2H 3 As0 3 = As 2 3 -f 3H 2 The aqueous solution of arsenious oxide, neutralized with ammonia, gives a green precipitate with solution of cupric sul- phate ; this is copper arsenite, or Scheele's green. With silver nitrate it gives a canary-yellow precipitate of silver arsenite. Arsenious oxide is more soluble in hydrochloric acid than in water. If a slip of clean copper be introduced into this solu- tion, it becomes covered with a steel-gray or black coating of arsenic. Reinsch's test for arsenic consists in boiling the suspected substance with dilute hydrochloric acid and bright metallic copper. The arsenic is deposited upon the copper, and by carefully heating the latter in a small tube the arsenic vola- tilizes and is converted into arsenious oxide, which condenses in the crystalline form, easily recognizable by aid of a micro- scope. By the action of zinc the solution of As 2 3 in hydrochloric acid disengages hydrogen arsenide ; the zinc displaces the hy- drogen of the hydrochloric acid, and, by the action of this nascent hydrogen upon the arsenious oxide, water and hydro- gen arsenide are formed. As 2 3 -f 6H 2 = 3H 2 -f 2AsH 3 ARSENIOUS OXIDE. 181 Marsh's Apparatus, The reducing action of nascent hy- drogen upon arsenious oxide is used for the detection of this substance by the aid of Marsh's apparatus. This consists of an apparatus for the generation of hydrogen (Fig. 72) ; it contains pure zinc arid dilute sulphuric acid, and the hydrogen burns at the drawn-out jet with an almost colorless flame. If, however, a few drops of a solution of arsenious oxide be in- troduced by the fun- nel-tube, the character of the flame is at once changed ; it becomes bluish, elongated, and diffuses a white smoke, and if a white porce- lain surface be de- pressed into it, large spots of a brownish color are produced. p These are composed of arsenic, which is set free in the interior of the flame by the decomposition of the hydrogen arsenide by the heat. FIG. 73. Fig. 73 represents a more perfect form of Marsh's appa- ratus. The hydrogen, mixed with the hydrogen arsenide, first 16 182 ELEMENTS OF MODERN CHEMISTRY. traverses a tube, B, filled with cotton, designed to arrest the small drops of liquid which may be carried with the gas ; it then passes through a narrow tube wrapped with metallic foil and heated to redness in a tube-furnace. The hydrogen arsen- ide is decomposed into hydrogen and arsenic, and the latter is deposited as a brilliant black mirror in the cooler portion of the tube. Marsh's apparatus permits the detection of the least trace of arsenious or arsenic acid in a liquid. It is of great value in medico-legal researches, as arsenious oxide is a common and dangerous poison. ARSENIC ACID Preparation. When arsenious oxide is heated with nitric acid having a specific gravity of 1.35, red vapors are disen- gaged and the oxide is oxidized into arsenic acid, which may be obtained as a syrupy liquid by sufficient concentration. When left for a long time in a cool place it deposits colorless crystals, which constitute a hydrate 2H 3 AsO* -f H 2 O (E. Kopp). These crystals are very deliquescent, and dissolve in water with the production of cold. They melt at 100, losing their water of crystallization, and there remains a mass com- posed of fine needles, which constitute the normal acid H 3 AsO. When heated for some time to a temperature between 140 and 180, this acid loses water, and is converted into pyro- arsenic acid, H 4 As 2 7 . 2H 3 AsO H 2 = H 4 As 2 7 Between 200 and 206 another quantity of water is driven out, and on cooling there remains a pasty, pearly mass, which is metarsenic acid, HAsO 3 . H 3 AsO* H 2 = HAsO 3 It will be noticed that in their modes of formation and in their constitution, arsenic, pyro-arsenic and metarsenic acids are analogous to the corresponding acids of phosphorus. When metarsenic acid is heated to dull redness, it loses all of its hydrogen in the form of water, and is converted into arsenic oxide, As 2 5 . 2HAs0 3 H 2 = As 2 5 COMPOUNDS OF SULPHUR AND ARSENIC. 183 At this temperature the oxide melts, and at a bright-red heat it is decomposed into arsenious oxide and oxygen. As 2 5 = As 2 3 -f O 2 When exposed to the air it absorbs moisture, but very slowly, and even when treated with water it requires a certain time for solution. Ordinary arsenic acid, which may be called, ortharsenic, is very soluble in water ; its solution strongly reddens blue litmus and possesses a very acid taste. It is reduced by nascent hydro- gen, like the solution of arsenious oxide. When neutralized with ammonia, it forms a bluish-white precipitate with solution of cupric sulphate, and a brick-red precipitate with silver nitrate. Hydrogen sulphide produces no immediate precipitate. A solution of sulphurous acid reduces arsenic acid to arse- nious oxide, and then on the addition of hydrogen sulphide, a yellow precipitate of arsenic sulphide, As 2 S 3 , is formed. COMPOUNDS OF SULPHUR AND ARSENIC. Three sulphides of arsenic are known: Arsenic disulphide, or realgar As 2 S 2 Arsenic trisulphide, or orpiment As ? S 3 Arsenic pentasulphide As 2 S 5 Arsenic Bisulphide, As 2 S 2 . This body occurs in nature in the form of transparent red crystals, which belong to the type of the oblique rhombic prism. It is obtained as a red mass having a conchoidal fracture by melting 75 parts of arsenic with 32 parts of sulphur. It is fusible, and may be crystallized by slow cooling. When strongly heated in closed vessels, it boils and distils without alteration, but when heated in the air, it burns into arsenious and sulphur- ous oxides. The alkaline sulphides and ammonium sulphide dissolve realgar, leaving a brown powder which has been con- sidered as a subsulphide of arsenic. Boiling solution of potas- sium hydrate also dissolves realgar, forming a mixture of potassium arsenite and sulpharsenite ; the latter is a soluble compound of arsenic trisulphide and potassium sulphide; a brown powder remains undissolved. Arsenic Trisulphide, or Orpiment, As' 2 S 3 . When a solu- tion of arsenious oxide is submitted to the action of hydrogen 184 ELEMENTS OP MODERN CHEMISTRY. sulphide, the liquid assumes a yellow color without the forma- tion of any precipitate, but if a drop of hydrochloric acid be added, a yellow, flocculent precipitate of arsenic trisulphide is formed at once. As 2 3 + 3H 2 S = As 2 S 3 -f 3H 2 The composition of arsenic trisulphide corresponds to that of arsenious oxide, and is the same as that of the orpiment found in nature. It may also be obtained by fusing together arsenic and sul- phur in the proper proportions, or even arsenious oxide and sulphur; in the latter case, sulphurous oxide is disengaged, and arsenic trisulphide sublimes. Thus prepared, orpiment occurs as crystalline masses of a yellow color, bordering upon orange, and a pearly aspect. Its density is 3.459. It is fusible and volatile. Arsenic trisulphide obtained by precipitation is insoluble in cold water, and but slightly soluble in boiling water, but it is very soluble in ammonia. By continued boiling with water, it yields hydrogen sulphide and arsenious acid (de Clermont and Frommel). It is also dissolved by solutions of the alka- line sulphides with the formation of sulpharsenites, compounds of two sulphides, in which the alkaline sulphide plays the part of a base and the arsenic trisulphide the part of an acid. Orpiment also dissolves in solutions of the caustic alkalies with the formation of an arsenite and a sulpharsenite. Arsenic Pentasulphide, As 2 S 5 . By the prolonged action of hydrogen sulphide upon a solution of arsenic acid, a pale- yellow precipitate is obtained, which is arsenic pentasulphide. 2H 3 AsO + 5H 2 S As 2 S 5 -f 8H 2 It corresponds to arsenic oxide. As 2 5 As 2 S 5 Arsenic oxide. Arsenic sulphide. The alkaline sulphides dissolve it with the formation of sulpharsenates. Among the latter there is one having the composition K 3 AsS*, and which corresponds to the arsenate K 3 As0 4 . It is formed by the following reaction : As 2 S 5 -f 3K 2 S = 2(K 3 AsS 4 ) The existence of arsenic pentasulphide has recently been questioned, the precipitated body seeming to be a mixture of trisulphide and sulphur (de Clermont and Frommel). ANTIMONY. 185 ANTIMONY. Sb = 122 Antimony is generally classed with the metals. It indeed possesses the lustre of a metal, and it conducts heat and elec- tricity; but in a true chemical classification these physical properties cannot overbalance the most striking chemical anal- ogies. By its affinities, and by the nature and constitution of its compounds, antimony must find a place by the side of arsenic, which must itself be classed with phosphorus and nitrogen. Metallurgy of Antimony. The most common ore of anti- mony, which is a sulphide, was known to the ancients. The metal is extracted from it by a very simple process. The sul- phide is first separated by fusion from the earthy materials, called gangue, with which it is associated ; it is then roasted or heated in contact with air. The sulphur is in great part expelled in the form of sulphurous oxide gas, and the antimony is converted into oxide, which still contains some undecom- posed sulphide. The whole is then pulverized, and the pow- der mixed with pulverized charcoal impregnated with sodium hydrate. This mixture is calcined in crucibles, and the anti- mony oxide and a portion of the sulphide is reduced by the charcoal ; sodium sulphide is also formed, and this dissolves a portion of the antimony sulphide, forming a flux which floats upon the molten antimony ; after cooling, the latter is found at the bottom of the crucible as a button, easy to separate from the scoriae. By another process the antimony sulphide is fused with metallic iron. Iron sulphide and antimony are formed, and the latter collects at the bottom by reason of its greater density. Perfectly pure antimony is prepared in the laboratory by reducing antimonous or antimonic oxide by charcoal. Properties. Antimony is a brilliant white metal, having a slightly bluish lustre ; it is brittle, and has a laminated frac- ture. Its density is 6.715. It melts at about 450, and sensibly vaporizes at a white heat. Antimony may be crystallized by allowing large masses of the fused metal to cool slowly, and decanting the liquid por- tion. Small acute rhombohedra may be obtained in this manner. 16* 186 ELEMENTS OP MODERN CHEMISTRY. When heated in contact with air. antimony is converted into antimonous oxide, Sb 2 3 . If a fragment of antimony be introduced into a cavity scraped in a piece of charcoal, and the flame of a blow-pipe be directed upon it, it melts, becomes red-hot, and gives off white fumes. If now the molten globule be allowed to fall, it breaks up into a multitude of smaller globules on striking the floor, and each particle rebounds into the air as a brilliant spark, leaving behind it a train of smoke. Powdered antimony projected into dry chlorine unites with that element, producing a brilliant combustion. HYDROGEN ANTIMONIDE. There is a compound of hydrogen and antimony which has not yet been obtained in the pure state, but which, according to all probability, is the body SbH 3 . Like its analogue, hy- drogen arsenide, it is decomposed by heat ; it can also be pre- pared in Marsh's apparatus by the action of nascent hydrogen upon a solution containing antimony, and when decomposed by heat it forms metallic rings and mirrors, which it is of im- portance to distinguish from those formed by arsenic. The following differences are sufficient for this purpose: The antimony rings are not displaced when heated in a current of hydrogen ; the arsenic rings are volatilized, and condense in a cooler portion of the tube. The spots and rings of antimony are not dissolved by a solu- tion of sodium hypochlorite (Labarraque's solution), which at once dissolves those of arsenic. The antimony spots are readily dissolved by a drop of nitric acid, and the liquid leaves on evaporation a white residue, which is not colored by the addition of a drop of silver nitrate solution. Under the same circumstances, the arsenical spots leave a white residue, which assumes a brick-red color when moistened with a solution of silver nitrate, owing to the for- mation of silver arsenate. COMPOUNDS OF ANTIMONY AND CHLORINE. Two chlorides of antimony are known : Antimony trichloride SbCl 3 Antimony pentachloride SbCl 5 Antimony Trichloride, SbCl 3 . This compound, formerly COMPOUNDS OF OXYGEN AND ANTIMONY. 187 known as butter of antimony, is formed by the action of hy- drochloric acid upon antimony sulphide. It is generally pre- pared in the laboratory from the residue from the preparation of hydrogen sulphide. This acid liquid is distilled in a retort provided with a receiver, which is changed as soon as the anti- mony chloride which distils over begins to crystallize in the neck of the retort. This chloride is solid, transparent, and colorless. It melts at 73.2, and boils at 230. It dissolves in water charged with hydrochloric acid, forming a colorless solution, but when this liquid is diluted with water there is formed an abundant white precipitate, long known as powder of Algaroth. It is an oxychloride of which the composition does not appear con- stant. There is one which contains SbOCl, and which can be regarded as antimony trichloride, in which two atoms of chlo- rine have been replaced by one atom of oxygen. It is form 3d by a double decomposition, according to the following reaction : SbCP + H 2 2HC1 -f SbOCl Antimony Pentachloride, SbCl 5 . This is formed by the action of an excess of chlorine upon antimony or upon the trichloride. It is a yellow liquid, giving off white fumes in the air. It is volatile, but cannot be distilled without undergoing a partial decomposition into chlorine and antimony trichloride. When exposed to the air, it absorbs moisture and is converted into a crystalline mass, which is a hydrate of the pentachloride. When treated with a large excess of water, it is decomposed with production of heat, and formation of pyrantimonic and hydrochloric acids. COMPOUNDS OF OXYGEN AND ANTIMONY. Two oxides of antimony are known, corresponding to those of phosphorus and arsenic : Antimonous oxide Sb2Q 3 Antiinonic oxide Sb 2 5 Normal antimonic acid, H 3 SbO*, corresponding to phosphoric and arsenic acids, is not known in the free state, but a derivative of this acid exists and may be regarded as antimony antimonate. Its composition is Sb 2 4 , and it is derived from antimonic acid 188 ELEMENTS OP MODERN CHEMISTRY. by the substitution of an atom of antimony for three atoms of hydrogen. H 3 Sb0 4 antimonic acid. SbSbO* antimony antimonate. There is a pyrantimonic and also a metantimonic acid, analogous to the corresponding phosphorus acids : H 4 Sb 2 7 pyrantimonic acid. HSbO 3 metantimonic acid. ANTIMONOUS OXIDE. Sb 2 3 This is obtained by oxidizing the metal in the air. The operation may be conducted in two crucibles placed one above the other, an opening being pierced in the upper one for the access of air. They are heated to redness in a furnace, and on cooling, the antimony is found to be partially converted into brilliant needles that the ancients called silver flowers of anti- mony. The crystals are right rhombic prisms, mixed with regular octahedra, for antimonous oxide crystallizes in two forms, presenting the same character of dimorphism as arsenious oxide. The two compounds are hence said to be isodimorphous. When solution of sodium hydrate, or better, sodium carbon- ate, is poured into solution of antimony trichloride, a white precipitate of antimonous hydrate is formed, and, in the latter case, carbonic acid gas is disengaged. SbCP + 3NaOH = H 3 Sb0 3 -f SNaCl Sodium hydrate. Antimonous hydrate. Sodium chloride. This hydrate readily parts with a molecule of water, being converted into another hydrate, HSbO 2 . H 3 Sb0 3 H 2 = HSbO 2 ANTIMONY ANTIMONATE. Sb 2 This compound is formed when antimonous oxide is heated for a long time in the air, oxygen being absorbed, or when antimonic oxide is strongly calcined, oxygen being then disen- gaged. It is a white, infusible powder, undecomposable by heat and insoluble in water. ANTIMONIC OXIDE AND ACIDS. 189 ANTIMONIC OXIDE AND ACIDS. When powdered antimony is heated with concentrated nitric acid, a white powder is obtained, which is metantimonic acid. It contains one atom of hydrogen capable of being replaced by an equivalent quantity of metal, and thus corresponds to meta- phosphoric acid. HPO 3 HSbO 3 KSbO 3 Metaphosphoric acid. Metantimonic acid. Potassium metantimonate. When it is heated to dull redness, it loses water and is con- verted into antimonic oxide. 2HSb0 3 H 2 t= Sb 2 5 If antimony pentachloride be poured into an excess of water, a white precipitate of pyrantimonic acid is formed. It is the analogue of pyrophosphoric acid, and, like the latter, contains four atoms of hydrogen. H*P 2 7 H 4 Sb 2 7 K*Sb 2 7 Pyrophosphoric acid. Pyrantimonic acid. Potassium pyrantimonate. According to Fremy, potassium pyrantimonate may be obtained by heating metantimonic acid or potassium metanti- monate with potassium hydrate, in a silver crucible. 2KSb0 3 + 2KOH = K 4 Sb 2 O 7 -f H 2 O Potassium Potassium Potassium metantimonate. hydrate. pyrantimonate. The metantimonate may be extracted by water, in which it is soluble, from the white mass, called by the ancients dia- phoretic antimony, which is obtained by deflagrating in a red- hot crucible a mixture of 2 parts of nitre (potassium nitrate) and 1 part of powdered antimony. Cold water first dissolves potassium nitrate from this mass, and then potassium metanti- monate. The solution of the latter salt produces with hydro- chloric acid a white precipitate of metantimonic acid. SULPHIDES OF ANTIMONY. Two sulphides of antimony are known : Antimony trisulphule, or antimonous sulphide . . Sb 2 S 3 Antimony pentasulphide, or antimonic sulphide . . Sb 2 S 5 Antimonous Sulphide, Sb 2 S 3 . This compound, ordinarily called sulphide of antimony, occurs both in the crystalline 190 ELEMENTS OF MODERN CHEMISTRY. form and amorphous. Crystallized, it exists in nature and is the mineral commonly known as stibium. It is separated from its gangue by fusion, and is thus obtained in gray masses com- posed of brilliant needles having a metallic lustre. Amorphous, it constitutes the orange-colored precipitate formed by the action of hydrogen sulphide upon a solution of antimony chloride. This precipitate is insoluble in ammonia, but dissolves in ammonium sulphide and in the alkaline sul- phides. Antimony trisulphide is reduced by hydrogen at a high temperature ; hydrogen sulphide is formed, and metallic anti- mony remains. When heated in the air, antimony sulphide is oxidized with formation of sulphurous oxide and antimonous oxide. The incompletely roasted residue melts at a red heat, and on cool- ing assumes the form of a brown vitreous mass called glass of antimony. It is an impure oxysulphide which appears to contain the compound Sb 2 S 2 = g^g j 0. Antimony Pentasulphide, Sb' 2 S 5 . When finely-pulverized antimony trisulphide is digested with sulphur and a solution of sodium hydrate, or a mixture of sulphur, sodium carbonate, and lime, the antimony sulphide gradually dissolves in the liquid, combining both with sulphur and with the sodium sul- phide formed. The product of the reaction is a sulphantimo- nate of sodium, which is deposited in fine crystals from 'the concentrated liquid. Sb 2 S 5 + 3Na 2 S = 2Na 3 SbS 4 Sodium sulphide. Sodium sulphantimonate. The crystals of this compound contain 9 molecules of water of crystallization. It corresponds to the sulpharsenate already mentioned, and to trisodium phosphate, Na 3 P0 4 . It is soluble in water, and on the addition of hydrochloric acid to its solution, hydrogen sulphide is disengaged and anti- mony pentasulphide is precipitated. 2Na 3 SbS* 6HC1 = GNaCl Sb 2 S 5 3H 2 S General Considerations upon the Elements of the Nitro- gen Group. Nitrogen, phosphorus, arsenic, and antimony, and bismuth might be added, form a group of elements allied by the most striking analogies. This is made manifest by the BORON. 191 atomic composition of their compounds, as will be seen in the following synopsis : HYDROGEN COMPOUNDS. NH 3 PH 3 AsH 3 SbH 3 Ammonia. Hydrogen phosphide. Hydrogen arsenide. Hydrogen antimonide. NCI 3 Nitrogen trichloride. CHLORINE COMPOUNDS. PCI 3 AsCl 3 Phosphorus trichloride. PCI 5 Arsenic trichloride. SbCP Antimony trichloride. SbCl 5 Phosphorus pentachloride. OXYGEN COMPOUNDS. Antimony pentachloride. As*O Sb 2 3 Nitrogen trioxide. Phosphorous oxide. Arsenious oxide. Antimonous oxide. N 2 5 P 2 5 As'O Sb 2 5 Nitrogen pentoxide. Phosphoric oxide. Arsenic oxide. Antimonic oxide. H 3 P0 4 Phosphoric acid. H 3 P0 3 H 3 As0 3 H 3 Sb0 3 Phosphorous acid. Arsenious acid. Antimonous acid. HNO 2 HSbO 2 Nitrous acid. Antimony I hydrate. H 3 As0 4 Arsenic acid. H 4 As 2 7 H 4 Sb 2 7 Pyrophosphoric acid. Pyro-arsenic acid. Pyro-antimonic acid. HNO 3 HPO 3 HAsO 3 HSbO 3 Nitric acid. Metaphosplioric acid. Metarsenic acid. Metantimonic acid. If the analogy between nitrogen and phosphorus were com- plete, there should be an orthonitric acid, H 3 N0 4 = HNO 3 -f- H 2 0, corresponding to ordinary or orthophosphoric acid. This acid is not known as a definite hydrate, but compounds exist which are derived from it. Thus, bismuth subnitrate, BiNO 4 , can be regarded as a salt of orthonitric acid, in which three atoms of hydrogen are replaced by one atom of triatomic bismuth. BORON. Bo = 11 Boron is the radical of boric acid. It exists in the amor- phous state and crystallized. It was discovered by Gay-Lussac and Thenard in 1808. 192 ELEMENTS OF MODERN CHEMISTRY. Preparation. 1. Amorphous Boron, Boric oxide is re- duced by sodium at a red heat, and the cooled mass is treated with dilute hydrochloric acid. The sodium borate which is formed is thus dissolved, and a residue consisting of amorphous boron is obtained as a dark powder. 2Bo 2 3 + 3Na 2 = 2Na 3 Bo0 3 + Bo 2 Boric oxide. Sodium. Sodium borate. 2. Crystallized Boron. Boric oxide is fused with alumin- ium ; a part of this metal reduces the boric oxide and becomes oxidized, while another part dissolves the boron set free, and again deposits it in the crystalline form on cooling (H. Sainte- Claire Deville), Al 2 + Bo 2 3 = APO 3 + Bo 2 Properties. Amorphous boron is a dark-brown powder, or brown bordering upon green. It is infusible. Heated to 300 in the air, it burns, being converted into boric oxide. Its combustion in pure oxygen is very brilliant. Amorphous boron possesses a singular affinity for nitrogen. At a red heat it absorbs this gas, forming a nitride of boron, BoN. When heated to dull redness in an atmosphere of nitrogen dioxide, it burns into a mixture of boric oxide and boron nitride (Wohler and Deville). Crystallized boron occurs as square octahedra (Sella). In this form it is almost as hard as the diamond, and will scratch rubies. The color of the crystals varies from yellow to deep garnet-red; sometimes they appear black. Their density is 2.63. Crystallized boron energetically resists oxidation, both when it is heated in oxygen and when it is subjected to the action of fused potassium nitrate. At a bright-red heat it reacts upon potassium acid sulphate, sodium hydrate, and sodium carbonate. It burns in chlorine at a red heat. BORON CHLORIDE. BoCl 3 Preparation. This body, which was discovered by Berze- lius, is prepared by Wb'hler and Deville by heating perfectly dry, amorphous boron in a current of chlorine gas, and passing the vapor of boron chloride formed into a receiver surrounded by a mixture of ice and salt. BORON FLUORIDE. BORIC ACID. 193 Properties. In a state of purity, boron chloride is a color- less, mobile, and highly-refractive liquid, boiling at 17. It fumes in the air, and is readily decomposed by water into boric and hydrochloric acids. BoCP -f 3H 2 = 3HC1 + Bo(OH) 3 BORON FLUORIDE. BoFl Density compared to air ........ 2.31 Density compared to hydrogen ...... 34. Preparation. Boron fluoride was discovered by Gay-Lussac and Thenard in 1810. It is prepared by heating in a glass retort an intimate mixture of one part of boric oxide and two parts of powdered calcium fluoride with twelve parts of sul- phuric acid. The gas disengaged is collected over mercury. 3CaFP + Bo 2 3 + 3H 2 SO* = 3CaS0 4 + 3H 2 + 2BoFP Calcium Boric oxide. Calcium sulphate. fluoride. Properties. Boron fluoride is a colorless gas, having a suf- focating odor. It produces abundant fumes in the air, and is very soluble in water, which dissolves about 800 times its volume of this gas. Its affinity for water is so great that it carbonizes paper and analogous organic substances, from which it removes the elements of water. The solution of boron fluoride in water is accompanied by a chemical reaction ; when the aqueous solution of this gas, satu- rated at the ordinary temperature, is cooled to 0, crystals of boric acid are deposited, and a very acid liquid is obtained, known as hydrofluoboric acid ; its composition is expressed by the formula : BoFl 4 H = BoFP.HFl BORIC ACID. Preparation. Boric acid was discovered by Homberg in 1702. It is found in the free state in the craters of certain volcanoes, and exists in solution in the lagoni of Monte- Rotondo, in Tuscany. These are muddy little lakes, through which arise the gaseous emanations from the fissures of a vol- canic soil. The gases (suffioni) contain sensible traces of boric i 17 194 ELEMENTS OF MODERN CHEMISTRY. acid, which is dissolved by the water of the lagoni. On evap- oration, this water furnishes the crude boric acid. Large quantities of borax (sodium borate) are obtained from Borax Lake and from Lake Clear, about two hundred and fifty miles north of San Francisco, California. The crude borax is extracted from a muddy deposit, which is obtained from the bottom of the lakes by dredging. In the laboratory, boric acid is prepared by decomposing a boiling saturated solution of borax or sodium borate with dilute sulphuric acid. The latter is added in small portions until the liquid strongly reddens litmus-paper ; the solution is then allowed to cool, and the boric acid separates in the crystalline form. Properties. Pure boric acid crystallizes in pearly scales, somewhat greasy to the touch. It dissolves in 25 parts of water at 18, and is much more soluble in boiling water. The solution is feebly acid, and changes blue litmus solution to a wine color. Boric acid dissolves in alcohol, and the solution burns with a green flame. When boric acid is heated in a platinum crucible to a tem- perature near redness, it loses all of its water, melts, and solidi- fies to a transparent glass on cooling. This is boric oxide. 2H 3 Bo0 3 = Bo 2 3 -f 3H 2 At a red heat this body dissolves a great number of solid sub- stances, particularly the metallic oxides ; it then yields variously colored glasses on cooling. Boric oxide is not decomposed by charcoal at a red heat, but if a current of chlorine be passed over an intimate mixture of boric oxide and charcoal, heated to bright redness in a porce- lain tube, boron chloride and carbon monoxide are formed (Dumas). Bo 2 3 + 3C -f 3C1 2 = 2BoCP -j- SCO SILICON. Si = 28 Like boron, silicon exists amorphous and in the- crystalline form. It was discovered by Berzelius in 1825. Preparation. 1. Amorphous Silicon. Well-dried sodium SILICON. 195 fluosilicate is heated with half its weight of metallic sodium : sodium fluoride is formed and silicon is set free. Na 2 FP.SiFl 4 + 2Na 2 == 6NaFl + Si Sodium fluosilicate. Sodium fluoride. On cooling, the mass is exhausted, first with cold, and after- wards with hot, water ; a brown powder of amorphous silicon remains. 2. Crystallized Silicon. Deville and Caron obtained crys- tallized silicon by projecting a mixture of 3 parts of potassium and silicon double fluoride, 4 parts of zinc, and 1 part of sodium into a red-hot crucible. Fluoride of sodium is formed, and the silicon set free dissolves in the zinc and separates in the crystalline form on cooling; it is isolated from the zinc by dissolving the button in hydrochloric acid ; the silicon remains in the form of brilliant laminae or needles. These crystals are of a dark steel-gray color, and possess a metallic lustre; they are composed of chaplets of regular octahedra. Properties. Amorphous silicon is a brown powder, more dense than water, in which it is insoluble, and producing dark stains on the fingers. When heated in the air. it takes fire and burns with a bright light into silicic oxide, SiO 2 . Crystallized silicon has a density of 2.49. It may be heated to redness in oxygen without taking fire, but when it is calcined with potassium carbonate the latter is decomposed with a vivid emission of light, potassium silicate being formed and carbon being set free. Crystallized silicon resists the oxidizing action of both potassium nitrate and potassium chlorate, but it dis- solves slowly in a boiling solution of potassium hydrate, hydro- gen being disengaged and potassium silicate being formed. It burns when heated to redness in an atmosphere of chlorine, silicon chloride being formed. HYDROGEN SILICIDE. Probable formula SiH* Preparation. This compound was discovered by Wohler and Buff in 1857. Magnesium silicide* is introduced into a two-necked bottle, which is then entirely filled with water that * Wohler prepares this silicide by fusing in a crucible a mixture of 40 parts of magnesium chloride, 35 parts of silicon and sodium double fluor- ide, and 10 parts of sodium chloride, these salts being previously mixed with 10 parts of sodium in minute frngraents. 196 ELEMENTS OF MODERN CHEMISTRY. has been recently boiled. One of the necks of the bottle is fitted with a funnel-tube which passes to the bottom of the bottle, while to the other is adapted a delivery-tube leading to the pneumatic trough ; this tube also should be completely filled with water so that there is not a single bubble of air in the whole apparatus. Concentrated hydrochloric acid is then introduced by the funnel-tube, and immediately reacts with the magnesium silicide, forming magnesium chloride, which dissolves, and hydrogen silicide, which is disengaged and must be collected in jars filled with recently boiled water. Properties. The gas thus obtained is not pure hydrogen silicide ; it contains an excess of hydrogen. It is colorless and insoluble in water from which the air has been expelled. Water containing air in solution oxidizes it. If bubbles of the gas be allowed to escape through the water of the trough, each bubble takes fire on coming to the surface, burning with a bright light and a little explosion, and producing a white smoke of silicic oxide. This smoke forms rings like those produced by hydrogen phosphide under the same circum- stances, but often colored brown % by a portion of silicon set free. The incomplete combustion of hydrogen silicide is accompa- nied by a brown deposit of amorphous silicon. At a red heat, hydrogen silicide is decomposed into hydrogen and silicon. SILICON CHLORIDE. SiCl* This compound is formed when silicon is heated to dull redness in a current of chlorine, or when a current of the latter gas is passed over an incandescent mixture of charcoal and silica. + C 2 -J- Cl 4 = SiCl 4 + 2CO Silicic oxide. Carbon monoxide. Preparation. Precipitated silica, lamp-black, and oil are intimately mixed into a stiff paste. This paste is made into little balls, which are put into a crucible, the cover of which is then luted on, and the whole is heated to redness in a furnace. When cool, the balls are introduced into a porcelain tube or a clay retort (Fig. 74), which is then heated to bright redness, while a current of carefully-dried chlorine is passed through. The silicon chloride and the carbon monoxide formed are SILICON FLUORIDE. 197 passed through two U tubes surrounded by a mixture of ice and salt. The silicon chloride is thus condensed. Properties. Silicon chloride is a volatile, colorless liquid, of an irritating odor. It fumes in the air. Its density is 1.52, and it boils at 59. It is instantly decomposed by water, silicic and hydrochloric acids being formed. A part of the silicic acid is precipitated FIG. 74. in the form of a jelly, while another part remains in solution. The latter is perhaps a hydrate corresponding to the chloride. SiCl 4 + 4H 2 = 4HC1 -f Si(OH) 4 There exists a tetrabromide of silicon, SiBr 4 , and a tetra- iodide, SiP, both corresponding to the chloride which has just been described. Friedel has recently discovered an iodide, Si 2 ! 6 , remarkable as belonging to an entirely new series. SILICON FLUORIDE. SiFl* Density compared to air 3.6 Density compared to hydrogen 52. Preparation. An intimate mixture of silicious sand and 17* 198 ELEMENTS OF MODERN CHEMISTRY. finely-powdered calcium fluoride, or fluor spar, is introduced into a glass flask (Fig. 75), and a sufficient quantity of sul- phuric acid is added to reduce the whole to a creamy consistence. A gentle heat is applied, and the gas disengaged may be col- lected over mercury. 2CaFl 2 -f 2H 2 SO* -f SiO 2 = 2CaSO -f SiFl* + 2H 2 Calcium fluoride. Silicic oxide. Calcium sulphate. FIG. 75. Properties. Silicon fluoride is a colorless, suffocating gas, producing white fumes when allowed to escape into the air. It may be liquefied by a low temperature and a strong pressure. On contact with water it is decomposed, silicic hydrate separat- ing in gelatinous flakes, and hydrofluosilicic acid being formed. 3SiFl 4 + 3H 2 = 2(H 2 Fl 2 .SiFl 4 ) -f H'SiO 8 Hydrofluosilicic acid. Hydrofluosilicic Acid. A saturated, aqueous solution of this acid is a highly acid liquid, fuming in the air, and evapo- rating slowly at 40 from a platinum-dish without leaving any residue. It is prepared by passing gaseous silicon fluoride into water under which is a layer of mercury. The delivery-tube must dip beneath the surface of the mercury, so that the silicon flu- oride can only come in contact with the water after passing through the metal ; otherwise the delivery-tube would become obstructed by the deposit of gelatinous silica. Hydrofluosilicic acid is employed as a reagent in the labora- tory. It precipitates the salts of potassium and sodium, form- ing insoluble fluosilicates, R 2 Fl 2 .SiFl*. SILICIC OXIDE AND ACIDS. 199 SILICIC OXIDE AND ACIDS. (SILICA.) Native State. Silicic oxide is widely diffused in nature. It occurs crystallized, as the different varieties of quartz ; amor- phous, as agate, chalcedony, cornelian, flint, etc. ; granulated, it is found in sandstones and the sand produced by their disaggre- gation ; in this case it is often mixed with variable quantities of alumina and oxide of iron. Rock-crystal is pure silicic oxide. It occurs as six-sided prisms, terminated by pyramids of six faces (Fig. *76). As hydrate, silica exists in various minerals, such as opal and hydrophane. It is also found in the form of pulverulent deposits and in solution in many running waters, in large proportion in the hot waters of the geysers in Iceland. Properties. Quartz is infusible at the highest furnace heats, but undergoes a viscous fusion when introduced into the flame of the oxyhydrogen blow- pipe. Neither carbon nor potassium is capable of reducing it, even at the highest temperatures. It is not attacked by acids, with the exception of hydrofluoric acid. Boiling alkaline solutions scarcely affect it, but the amor- phous varieties of silica, such as flint, as well as opal and the other hydrates, dissolve more readily in boiling solutions of the alkaline hydrates. All of the varieties of silica, when heated to redness with the alkalies or alkaline carbonates, combine with the bases, forming silicates which enter into fusion at a high temperature and solidify to a vitreous mass on cooling. Potassium silicate, or soluble glass, is a transparent mass, soluble in water. When hydrochloric acid is added to this solution, potassium chloride is formed and silicic acid is precipitated as a gelatinous mass, which is not insoluble in water. An aqueous solution of silicic acid may be obtained. If hydrochloric acid be added to a dilute solution of potas- sium silicate, the liquid remains transparent although it contains silicic acid. It may be poured into a dialyser, composed of a piece of parchment-paper stretched over a wooden or glass ring, and floated on the surface of pure water contained in another vessel. The potassium chloride gradually passes through the 200 ELEMENTS OF MODERN CHEMISTRY. membrane, as would any crystallizable body, and the silicic acid remains alone dissolved in the water in the dialyser, as all other amorphous bodies which are soluble in water would do. Graham gave the name dialysis to this separation of crys- tallizable bodies, which he named crystalloids, from uncrystal- lizable bodies, which he named colloids, by means of certain membranes. The former bodies pass through the membranes, which are, however, impermeable to the colloids. The silicic acid which remains in solution probably consti- tutes normal silicic acid, H 4 Si0 4 == SiO 2 -f 2H 2 0. This hydrate is not known in the pure state. Ebelmen has described a hydrate, H 2 Si0 3 , which may be considered as the first hydrate of silicic oxide. H 4 Si0 4 H 2 = H 2 Si0 3 H 4 Si0 4 2H 2 = SiO 2 There are other silicic hydrates having more complex com- positions. Uses. Silica is largely employed in all of its various forms. Crystallized quartz, or rock crystal, is used for the manufacture of ornaments, spectacle-glasses, and lenses. Chalcedony, onyx, and opal are sought for by the lapidary and engraver. Agate, which is very hard, is used for the manufacture of mortars, etc. Sandstones serve for building purposes and for grindstones; sand, for mortars and the manufacture of glass and pottery. CARBON. = 12 Natural State and Varieties. The carbon of chemists is pure charcoal. This substance is known to all ; black, friable, light, absolutely fixed, inalterable by the air at ordinary tem- peratures, but combustible when heated in the air, it results from the calcination of organic matters, and particularly wood, in closed vessels. But carbon by no means always reveals these same properties. It occurs in nature under forms so different that it is impossible to apply a general description to all of its known varieties. What could be more different, as far as physical properties are concerned, from the soot deposited by a smoky flame, or the light, porous, and opaque charcoal, than the hard, dense, and transparent substance found in nature CARBON. 201 in the form of diamond ? Nevertheless, these bodies are com- posed of one and the same substance, carbon ; alike, they all burn in oxygen at a high temperature, producing carbonic acid gas. Among the various forms which carbon assumes, and which constitute one of the most curious examples of dimorphism, the following may be described : Diamond. This is the hardest of all bodies ; it scratches all others, and can only be trimmed by grinding with its own dust. It is found crystallized in the form of the regular octahe- dron and the modifications thereof, among which must be men- FIG. 77. tioned the polyhedra of twenty-four and forty-eight faces. The faces are generally convexly curved (Fig. 7f ) The density of the diamond is between 3.50 and 3.55. It is a bad conductor of heat and electricity ; it strongly refracts and disperses light. From this latter fact Newton first divined its combustible nature, which was proved, in 1694, by the Floren- tine academicians of del Cimento, who burned a diamond in the focus of a concave mirror. Lavoisier and Davy repeated this celebrated experiment. Exposed to the high temperature of the voltaic arc between two carbon poles in a vacuum, the dia- mond swells up, blackens, and is converted into a substance analogous to coke ( Jacquelain). Graphite, or Plumbago. This is a crystalline variety of carbon, which is found in primitive rocks in brilliant steel-gray foliated masses. It sometimes occurs in hexagonal laminae. It can be scratched with the finger-nail, and leaves a black trace when drawn over paper. Its density is 2.2, and it con- ducts heat and electricity. It burns only at very high tem- peratures; ordinarily, it contains from one to two per cent, of foreign matters, i* 202 ELEMENTS OP MODERN CHEMISTRY. It has been obtained artificially. Melted iron possesses the property of dissolving carbon at a very high temperature, and again depositing it on cooling in the form of hexagonal scales of graphite. Plumbago is used for the manufacture of lead-pencils and crucibles, and is called black lead. There are other natural varieties of carbon, but they are far from presenting the same degree of purity as diamond or graphite. They are: Anthracite, a hard and compact variety of carbon containing from 8 to 10 per cent, of earthy matters. Bituminous coal, a brilliant, black variety, strongly impreg- nated with bituminous and earthy matters. It has been pro- duced by the slow decomposition of vegetable matters buried in the earth in the early geological ages. This origin is indi- cated by the impressions of leaves, stems, and fruits, which are evident in certain specimens of this coal. It contains only from 75 to 88 per cent, of carbon. When it is calcined in closed vessels, it disengages combustible gases and products which may be condensed in the liquid form and then separate into two layers. One is aqueous and ammoniacal, while the other is composed of tar. The residue of the distillation of bituminous coal is coke. The interior walls of the cast-iron vessels in which coal is distilled become covered with a com- pact layer of a gray, dense, hard and sonorous carbon, which is a good conductor of heat and electricity. This is the carbon of gas-retorts, and is produced by the igneous decomposition of hydrocarbons rich in carbon, which are disengaged during the calcination of the coal. Fat coals are those which burn with a long flame, softening in burning ; dry coals burn with a short flame which produces less heat than the preceding. Lignite is a combustible mineral containing less carbon, and more impure than bituminous coal ; it is found in the lower tertiary formations. Natural jet, which is employed for the manufacture of ornaments, is a variety of lignite. Among the artificial carbons, independently of coke, may be mentioned wood charcoal, lamp-black, and animal char- coal. Wood Charcoal. When wood is calcined in closed vessels it leaves a residue which is ordinary charcoal. It is prepared on the large scale by two processes, carbonization in stacks, CARBON. 203 which is carried on in the forests, and distillation in closed vessels. Charcoal is amorphous, brittle, and sonorous, a bad conductor of heat and electricity. Its density does not exceed 1.57. The lighter varieties are the more combustible. Its combustion leaves a residue of one or two per cent, of cinders, formed principally of mineral salts, among which the most abundant are the carbonates of calcium and potassium. FIG. 78. Lamp-Hack is produced by the incomplete combustion of organic substances rich in carbon. When rosin or tallow is burned, a dense smoke is produced which is composed of par- 204 ELEMENTS OF MODERN CHEMISTRY. tides of carbon that have escaped combustion. In the arts, lamp-black is procured by burning rosin in cast-iron pots, C (Fig. 78), heated by a fire, F. The vapors given off' are ig- nited, and the smoke is conducted into a chamber, A, the walls of which are hung with canvas. On this the lamp-black is de- posited, and is detached by lowering the cone B, which acts as a scraper. Lamp-black is not pure carbon. It contains tarry and oily matters, from which it may be freed by calcination in a covered crucible. It is used for the manufacture of printing- inks. Animal charcoal is produced by calcining animal matters, such as blood, the debris of skin, horn, bone, etc., in closed vessels. Bone-black or ivory-black contains the calcareous salts, calcium phosphate and carbonate, which form the base of the osseous tissue. The carbon is consequently disseminated through a porous mass. These salts may be extracted by treating the bone-black with dilute hydrochloric acid, by which they are dissolved. The residue, washed with water and dried, is known as washed or purified animal charcoal. Absorbent Properties of Charcoal. The amorphous and porous varieties of carbon, of which several forms have been described, possess the property of absorbing and retaining in their pores, gases, liquid and solid bodies. It is to this absorp- tive faculty that are due the decolorizing and disinfecting properties of charcoal, which are made use of to a large extent in the arts. If a piece of incandescent charcoal be plunged into mercury that it may cool out of contact with the air, and then be intro- duced into a small jar filled with ammonia or hydrochloric acid over the mercury-trough, the gas is at once absorbed and the mercury rises in the jar. The following table, by Th. de Saussure, indicates the quan- tities of several gases which are absorbed by one volume of charcoal : 1 volume of charcoal absorbs 90 volumes of ammonia. 85 65 55 40 35 9.42 9.25 7.50 1.75 hydrochloric acid, sulphurous oxide, hydrogen sulphide, nitrogen monoxide, carbon dioxide, carbon monoxide, oxygen, nitrogen, hydrogen. CARBON. 205 Charcoal increases in weight when exposed to the air, for it absorbs and condenses the atmospheric moisture. When plunged into water charged with a small quantity of hydrogen sulphide, it absorbs that gas and removes the odor of the water. The disinfecting properties of charcoal are thus easily explained. It is well known that charcoal will remove the unpleasant odor of corrupted waters, of meats slightly spoiled, and in general of organic matters in a state of putrefaction. A layer of char- coal between two layers of sand is an excellent filter for the clarification of drinking waters. The decolorizing properties of charcoal are another mani- festation of this general faculty of absorption, which is pos- sessed in the highest degree by animal charcoal. If litmus solution or red wine be agitated with a sufficient quantity of animal charcoal and subsequently filtered, the liquids pass through colorless. FIG. 70. This property of animal charcoal is largely applied in the arts, particularly for decolorizing sugars and syrups. Chemical Properties. Carbon is distinguished by its powerful affinity for oxygen, an affinity which is not, however, 18 206 ELEMENTS OF MODERN CHEMISTRY. exercised except at high temperatures. It only combines with oxygen at a red heat, and remains incandescent as long as com- bination goes on, the heat produced by the combination being sufficient to maintain the incandescence. In pure oxygen it burns with a brilliant light. The product of the combustion is carbonic acid gas. By the aid of heat, carbon decomposes a great number of oxygenized compounds, removing and combining with the whole or a part of their oxygen. This decomposition takes place at comparatively low temperatures when the oxygenized body does not strongly retain its oxygen ; in this case, carbon dioxide is formed, and the reduction of cupric oxide by char- coal furnishes an example. In the contrary case, the reduction, that is, the decomposition of the oxidized body, requires a very high temperature ; carbon monoxide is then formed. The re- duction of zinc oxide by charcoal is an example. If an incandescent charcoal be rapidly plunged under a bell- jar filled with water on the pneumatic trough, bubbles of gas arise and collect in the jar (Fig. 79). They are formed of a mixture of hydrogen, carbon monoxide, and a small quantity of carbon dioxide. These gases are produced by the decom- position of the water by the charcoal, which was red-hot at the moment of contact with the liquid. C -f H 2 = H 2 -f CO carbon monoxide. Carbon combines directly with sulphur at a high tempera- ture, forming carbon disulphide. COMPOUNDS OF CARBON AND OXYGEN. Two compounds of carbon and oxygen are known : Carbon monoxide . . CO Carbon dioxide, or carbonic acid gas CO 2 The latter body, which has long been known as carbonb acid, is the oxide corresponding to the true carbonic acid, which would be CO 2 + H 2 = H 2 C0 3 This normal carbonic acid is as yet unknown : it is doubtless too unstable to exist in the free state. However, its existence CARBON MONOXIDE. 207 may be admitted, for a corresponding compound is known in sulphocarbonic acid H 2 CS 3 . CARBON MONOXIDE. Density compared to air 0.967 Density compared to hydrogen 14. Molecular weight CO =28. Preparation. 1. An intimate mixture of zinc oxide and charcoal may be calcined in a clay retort. ZnO + C = CO + Zn 2. A convenient method of preparing carbon monoxide con- sists in heating oxalic acid with an excess of sulphuric acid in a glass flask. The oxalic acid loses the elements of water, which it yields to the sulphuric acid, and breaks up into carbon dioxide and carbon monoxide. C 2 H 2 0* = CO 4- CO 2 + Oxalic acid. Carbon monoxide. Carbon dioxide. H 2 O FIG. 80. The mixture of the two gases is passed through a wash-bottle, B (Fig. 80)", containing a solution of potassium hydrate, by 208 ELEMENTS OF MODERN CHEMISTRY. which the carbon dioxide is absorbed, potassium carbonate being formed. Carbon monoxide alone passes through, and may be collected over water. Properties. Carbon monoxide is a colorless, odorless gas. It is neutral, and does not trouble lime-water, which distin- guishes it from carbon dioxide. It extinguishes burning bodies, but is combustible itself, burning in the air with a blue flame, and forming carbon dioxide. It is not only unfit for respira- tion, but is very poisonous. Composition. If two volumes of carbon monoxide be mixed with one volume of oxygen in an eudiometer, and a spark be passed, complete combustion takes place, and the three volumes of the primitive mixture are reduced to two volumes of carbon dioxide. This can be verified by passing into the eudiometer a solution of potassium hydrate, which will completely absorb the new gas. It hence follows that two volumes of carbon monoxide con- tain the same quantity of carbon as two volumes of carbon dioxide. Knowing from other circumstances that two volumes of carbon dioxide contain two volumes of oxygen, it follows that two volumes of carbon monoxide contain one volume of oxygen. Its composition is then expressed by the formula CO 2 volumes. Carbon monoxide undergoes dissociation at a very high tem- perature. By operating under special conditions, H. Sainte- Claire Deville has succeeded in resolving it into carbon and oxygen. It is almost insoluble in water, but is absorbed by a solution of cuprous chloride in hydrochloric acid (Doyere and F. Le Blanc). Advantage is taken of this property in volumetric analysis to separate carbon monoxide from certain other gases. When heated for a long time to 100, in sealed tubes with potassium hydrate, it combines with the alkali, forming potas- sium formate (Berthelot). CO -|- KOH = KCHO 2 Potassium hydrate. Potassium formate. It is a beautiful synthesis of formic acid, so named because it exists in ants. Action of Chlorine upon Carbon Monoxide. Under the influence of sunlight, carbon monoxide combines directly with chlorine, forming a gas which is known as chloro-carbonic oxide, CARBON DIOXIDE. 209 or carbonyl chloride. It was formerly called phosgene gas. One volume of carbon monoxide combines with one volume of chlorine to form one volume of carbonyl chloride, so that the density of the latter is equal to the sum of the densities of carbon monoxide and chlorine. Compared to Hydrogen. Compared to Air. Density of carbon monoxide . . 14. 0.967 Density of chlorine 35.5 2.44_ Density of carbonyl chloride . 49.5 8.407 At ordinary temperatures, carbonyl chloride is a colorless gas, having a suffocating odor that provokes tears. At a low temperature, it condenses to a colorless liquid, boiling at 8.2 (Emmerling and Lengyel). It is instantly decomposed by water, with the formation of carbon dioxide and hydrochloric acid. COOP + H 2 = 2HC1 + CO 2 Its mode of formation, its composition, and its properties indicate its relations to carbon dioxide. 2 volumes CO absorb 2 volumes of chlorine to form 2 volumes CO.C1 2 2 volumes CO absorb 1 volume of oxygen to form 2 volumes CO.O It is seen that carbon monoxide plays to a certain extent the part of a radical ; it combines directly with oxygen or with chlorine to form either oxide or chloride of carbonyl. It is seen also that carbonyl chloride represents carbon dioxide in which one atom of oxygen is replaced by two atoms of chlorine. CARBON DIOXIDE. Density compared to air 1.529 Density compared to hydrogen 22. Molecular weight CO 2 =44. This gas was discovered by Black in 1648, and its composi- tion was recognized by Lavoisier in 1776. It is one of the constituents of the atmosphere, and is the product of a great number of reactions which take place on the earth's surface, such as the combustion of carbon and organic matters, respira- tion, and the phenomena of putrefaction and fermentation. It issues from the soil of volcanic countries. 18* 210 ELEMENTS OF MODERN CHEMISTRY. Preparation. Fragments of marble, which is calcium car- bonate, are intro- duced into a two- necked bottle fitted with a delivery- tube and a safety- tube (Fig. 81). The bottle is half- filled with water, and hydrochloric acid is gradually added by the fun- nel-tube. An ef- fervescence imme- diately takes place, due to the disen- gagement of car- bon dioxide. CaCP -f H 2 FIG. 81. CO 2 CaCO 3 -f 2HC1 == Calcium carbonate. Calcium chloride. The gas is most conveniently collected by dry downward displacement, like chlorine. Composition. 1. If carbon be burned in oxygen, the latter is converted into carbon dioxide without changing its volume. Hence two volumes of carbon dioxide contain two volumes of oxygen. These two volumes of oxygen, which represent two atoms, are combined with one atom of carbon, and the compo- sition of a molecule of carbon dioxide is hence expressed by the formula CO 2 == 2 volumes. 2. Dumas and Stas determined the centesimal composition of carbon dioxide by burning a known weight of diamond in oxygen, and carefully weighing the carbon dioxide produced. By subtracting the weight of the diamond burned from that of the carbon dioxide, the weight of the oxygen was determined. The apparatus employed is represented in Fig. 82. The increase in weight of the tubes L, M, N, 0, P indicates the quantity of carbon dioxide formed. Dumas and Stas thus found that 100 parts of carbon dioxide contain Carbon 27.27 Oxygen 72.73 100.00 CARBON DIOXIDE. 211 212 ELEMENTS OF MODERN CHEMISTRY. a centesimal relation which is expressed more simply by the numbers Carbon 12 Oxygen . 32 44 12 being the weight of one atom of carbon, and 32 the weight of two atoms of oxygen. Physical Properties. Carbon dioxide is colorless ; it has a feeble, somewhat pungent odor. A litre of this gas at 0, and under the pressure of 760 millimetres, weighs 1.966 grammes. FIG. 83. It is not permanent. Faraday succeeded in liquefying it at a temperature of 0, under a pressure of 36 atmospheres. The apparatus which is now used for its liquefaction is represented in Fig. 83. It is composed of two reservoirs, A and B, com- CARBON DIOXIDE. 213 municating by the metallic tube ?", furnished with a stop-cock at each end. The cylinders are made of heavy cast-iron, and are further strengthened by forged iron bands forced over their circumference. Each cylinder is movable on a horizon- tal axis, h. B is the generator; into it are introduced 1800 grammes of sodium dicarbonate, and a cylindrical copper tube, D, containing 1000 grammes of ordinary sulphuric acid. The cylinder is then closed by a strong screw plug, and a few oscil- lating movements are given to it in order that the sulphuric acid may gradually run out upon the sodium dicarbonate. Carbon dioxide is disengaged and is liquefied by its own press- ure as it accumulates in the apparatus. By the effect of the chemical action the temperature is raised to 30 or 40, and, communication being established between the two cylinders, the carbon dioxide distils rapidly into the receiver, the tem- perature of which is about 15. The operation is repeated several times, that one or two kilo- grammes of the liquid may accumulate in the receiver. A tube passes to the bottom of this vessel, and on opening the stop-cock which closes the superior extremity of this tube, a jet of the liquid is thrown out with force ; it is received tangently in a metallic box, A, A' (Fig. 84), having very thin sides. In this a portion of the oxide solidifies by reason of the great depression of temperature produced by the change of another portion into the gaseous state. A glittering-white, flaky mass collects in the receiver, having the appear- ance of snow. This is solid carbon dioxide. It is a bad conductor of heat and electricity, and can be ex- p IG g4 posed to the air for a few minutes before it disappears. In reassuming the gaseous form, it pro- duces an intense cold. If it be mixed with ether, the mixture, which is less porous and a better conductor of heat, can produce a lowering of temperature as great as 90. By pouring it upon mercury, large masses of that metal may be frozen. Drion and Loir have recently succeeded in collecting and maintaining carbon dioxide in the liquid state. It is colorless and mobile; has a density of 0.72 at +27, and 0.98 at 8. 214 ELEMENTS OF MODERN CHEMISTRY. This considerable difference between the densities is due to the enormous dilatation which the liquid undergoes between these limits of temperature. Indeed, ten volumes of liquid carbon dioxide at occupy fourteen volumes at 30. The coefficient of dilatation of the liquid is then superior to that of the gas. Carbon dioxide is incombustible, and extinguishes burning bodies. If carbon dioxide be poured from one vessel into another containing a lighted candle, it falls upon the flame like water, extinguishing it at once (Fig. 85). Lime-water poured into a jar of carbon dioxide becomes clouded, owing to the formation of insolu- ble calcium carbonate, These experiments permit the easy recognition of carbon dioxide from carbon monoxide. Carbon dioxide dissolves in its own volume of water at 15 under the normal pressure. If the press- ure be increased, the solubility of the gas is increased in the same proportion. Thus, under a press- ure of ten atmospheres one litre of water will dissolve ten litres of carbon dioxide ; but it must be remembered that under a press- ure of ten atmospheres these ten litres are reduced to one litre. Thus, one litre of water, which dissolves one litre of carbon dioxide at the ordinary pressure, dissolves also one litre under a pressure of ten atmospheres, and it may be said that water always dissolves its own volume of carbon dioxide, whatever may be the pressure. Water saturated with carbon dioxide under strong pressure, disengages a portion of the gas as soon as the pressure is removed. Such water is universally known and consumed in large quantities under the name of gaseous water or soda water. The solution of carbon dioxide exercises a much more ener- getic solvent action upon certain substances than pure water. It dissolves calcium carbonate, forming a soluble dicarbonate; it is even capable of dissolving calcium phosphate, transform- ing it into acid phosphate, which is soluble. Carbon dioxide is more soluble in alcohol than in water. FIG. 85. CARBON BISULPHIDE. 215 It is undecomposable by heat alone, but may be decomposed or reduced at high temperatures by contact with bodies avid of oxygen. Such substances are hydrogen and carbon. With the latter body the reduction takes place at a red heat, giving rise to the formation of carbon monoxide, the volume of which is double that of the carbon dioxide employed. CO 2 + C 2CO Carbon dioxide (2 vols.). Carbon moaoxide (4 vote.). CARBON BISULPHIDE. CS 2 This body is prepared by passing sulphur vapor over incan- descent charcoal. In the arts, the operation is conducted in cylindrical, cast-iron vessels, filled with charcoal and heated to redness, into which sulphur is introduced. The carbon disul- phide distils, and is condensed in a suitable cooling apparatus. Carbon disulphide is a colorless, very mobile, and highly-re- fracting liquid. Its odor is strong and unpleasant. Its density at 15 is 1.271, and it boils at 46. It is very inflammable, and burns with a blue flame, producing sulphurous oxide and carbon dioxide. CS 2 + O 6 = 2S0 2 + CO 2 Its vapor, mixed with oxygen, explodes on the application of flame. Carbon disulphide corresponds in composition to carbon dioxide. CO 2 carbon dioxide. CS 2 carbon disulphide. It is also analogous to the latter body in its chemical func- tions. While carbon dioxide combines with metallic oxides, forming carbonates, carbon disulphide combines with metallic sulphides, forming sulphocarbonates. CO 2 + Na 2 O = Na 2 C0 3 corresponding to H 2 C0 3 Sodium oxide. Sodium carbonate. Carbonic acM (bypothetical). CS 2 + Na 2 S = Na 2 CS 3 corresponding to H 2 CS 3 Sodium sulphide. Sodium sulphocarbonate. Sulphocarbonic acid. Sodium carbonate and sulphocarbonate possess the same con- stitution. By the action of strong acids they should give anal- ogous products: the one, carbonic acid, H 2 C0 3 ; the other, 216 ELEMENTS OF MODERN CHEMISTRY. sulphocarbonic acid, H 2 CS 3 . The latter body is indeed formed under such circumstances, but normal carbonic acid, if it exist, possesses no stability, and at once decomposes into carbon diox- ide and water. H 2 C0 3 *= CO 2 + H 2 Carbon disulphide is employed in the arts in the manufac- ture of vulcanized caoutchouc, and as a solvent for caoutchouc in the fabrication of goods impermeable to water by the deposit of a thin layer of that substance. It is also employed as a solvent for, and in the extraction of, fats and oils. CARBON OXYSULPHIDE. Density compared to air 2.1046 Density compared to hydrogen 30.4 Molecular weight CSO =60. This body was discovered by de Than in 1867. It is inter- mediate between carbon dioxide and carbon disulphide. COO carbon dioxide. CSO carbon oxysulphide. CSS carbon disulphide. Preparation. It is prepared by decomposing potassium sul- phocyanide by dilute sulphuric acid. Potassium sulphate and hydrosulphocyanic acid are formed, and, in the presence of an excess of sulphuric acid and water, the latter decomposes into ammonia and the gas carbon oxysulphide which may be collected over mercury; the ammonia remains combined with the sul- phuric acid in the form of sulphate. CSNH + H 2 = NH 3 + CSO Hydrosulphocyanic acid Carbon oxysulphide. Properties. Carbon oxysulphide is a colorless gas, having an odor like that of carbon disulphide, but also recalling that of hydrogen sulphide. On contact with an incandescent body, even a match pre- senting a spark of fire, it takes fire, burning with a blue flame, and depositing sulphur if the supply of air be insufficient. With one and a half times its volume of oxygen it constitutes an explosive mixture. 2 volumes of carbon oxysulphide . . = CSO mixed with 3 volumes of oxygen . = O 3 yield 2 volumes of carbon dioxide . = CO 2 and 2 volumes of sulphur dioxide . . . . = SO 2 COMPOUNDS OP CARBON AND HYDROGEN. 217 Water dissolves about its own volume of carbon oxysulphide, but the solution decomposes in a few hours, with the formation of hydrogen sulphide and carbon dioxide. CSO + H 2 = CO 2 + H 2 S Carbon oxysulphide is absorbed completely, but more slowly than carbon dioxide, by solutions of the alkaline hydrates ; by a reaction analogous to the preceding, a sulphide and a carbonate are formed. COMPOUNDS OF CARBON AND HYDROGEN. These compounds are numerous and important. Carbon unites with hydrogen in different proportions, and the atoms of carbon and hydrogen may accumulate in considerable numbers in the molecules of their compounds. These combinations are called hydrocarbons or carbides of hydrogen. Hydrogen mono- carbide, or marsh gas, contains only one atom of carbon com- bined with four atoms of hydrogen ; its molecule is therefore represented by the formula CH*. Tn olefiant gas, or ethylene, two atoms of carbon are united with four atoms of hydrogen ; in the volatile liquid known as benzine or benzol, which is ob- tained in large quantities from coal-tar, six atoms of carbon are combined with six atoms of hydrogen. Lastly, the molecule of oil of turpentine contains ten atoms of carbon and sixteen of hydrogen. Hence these substances give us the following formulae : CH 4 methane, or marsh gas. C 2 H* ethylene, or olefiant gas. C 6 H 6 benzine. C 10 H 16 turpentine. These examples, which might be indefinitely multiplied, show : 1st. That the atoms of carbon unite in various proportions with the atoms of hydrogen to constitute the molecules of the hydro- carbons. 2d. That they accumulate in greater or less numbers to form molecules more and more complex, that is, containing an increasing number of atoms of carbon and hydrogen. All of these bodies must be considered among the organic compounds ; indeed, the latter are nothing more than the com- pounds of carbon, and carbon monoxide and dioxide may also be properly considered as the most simple organic combinations. K 19 218 ELEMENTS OF MODERN CHEMISTRY. Hence if the most strictly rigorous method were adhered to, the description of the compounds of carbon and oxygen would be followed by that of all the other compounds of this element, that is, of all the organic compounds. However, for the pur- poses of study it is advantageous to treat the latter bodies separately, and they will be so considered in this work. The following experiments will expose some of the general proper- ties of the hydrocarbons which have been mentioned : 1. If a lighted taper be applied to a jar of methane, which is also called marsh gas, because it is disengaged from the muddy bottoms of marshes, the gas takes fire and burns with a lumi- nous flame. 2. If the same experiment be repeated with ethylene gas, which contains for the same proportion of hydrogen twice as much carbon as marsh gas, a still more luminous flame results. 3. It is well known that benzine and turpentine take fire when lighted, and burn with bright flames ; but it is also known that their flames are smoky. The hydrocarbons are then combustible; and how could they be otherwise, since they contain only two combustible elements, carbon and hydro- gen? The products of the combustion are water and carbon dioxide, and the forma- tion of the latter gas may be proved by agitating the con- tents of the jars in which the combustion has taken place with lime-water; the latter immediately becomes milky by the precipitation of calcium carbonate. This combustion is more or FIG. 86. less complete ; when the gas or vapor which burns contains a large amount of combustible elements, the oxygen of the air may not be present in sufficient quantity to burn them all, that is, to oxidize them completely. Under these conditions it is the hydrogen which is burned by preference, and the carbon partly escapes combustion. STRUCTURE OF FLAME. 219 A flame is a gas or vapor in combustion. This combustion is an oxidation, and it is the oxygen of the air which is the agent. In order that it may take place, it is generally neces- sary that the combustible gas shall be brought to a high tem- perature; but once commenced, the combustion continues of itself, because the heat disengaged by the oxidation is sufficient to maintain the phenomenon. But if a flame be suddenly cooled, the combustion is at once arrested. A flame may be cooled by depressing into it a piece of fine wire gauze. The incandescent gases cannot pass through the meshes of the gauze without being cooled by contact with the metal, which is a good conductor of heat. For this reason, no combustion takes place above the gauze (Fig. 86). If a piece of wire gauze be held over an escaping jet of gas, the latter may be ignited above the gauze, and will burn without the combustion being propagated to the gas below ; the gauze acts as a screen, separating the jet into two portions, the lower cold and invisible, the upper in combustion and luminous. Sir Humphry Davy made a happy ap- plication of these facts in the construction of the miner's safety-lamp. This is an ordinary lamp surrounded by a cylinder of wire gauze (Fig. 87). Such a lamp gives less light than one not protected by an envelope, but it re- moves the danger of explosions of fire- damp, for when an explosive mixture is p lf , 7 formed in the galleries of a mine, the gas may penetrate to the interior of the lamp and take fire there, but the flame cannot pass through the cooling envelope of wire gauze. The safety-lamps are now constructed with the lower part of the cylinder of glass, so that there is no diminution in the amount of light given. As the oxidation of combustible elements is the source of heat, it is evident that the different parts of a flame cannot be 220 ELEMENTS OF MODERN CHEMISTRY. uniformly hot, for the oxygen of the surrounding air cannot equally attain all portions. The exterior borders are the most intensely heated; they are surrounded by air, and constitute the seat of combustion. From them the heat is radiated not only externally, but also to the interior of the flame, where it produces interesting phenomena. These may be studied by analyzing a flame, that is, considering separately the different parts of which it is composed. If the flame of a can- dle be examined, it will be found to present three distinct layers, or cones (Fig. 88). 1. A dark central part, a, which surrounds *^e w i c k- This is known as the obscure cone, or cone of generation; its temperature is not high. 2. A luminous part, bb f , surrounding the ob- scure cone. This is the centre from which the light is emitted. It is known as the luminous cone, or cone of decomposition. 3. An exterior envelope, cc', thin, and pro- ducing but little light, yellow towards the sum- mit, 6j and bluish towards the base, dd'. It is the cone of complete combustion, and its temperature is the highest. It is easy to account for these phenomena. The material of the candle is melted by the heat Fio. 88. f tne flame, the liquid is drawn up into the wick by capillarity, and arrives at the incan- descent summit. There it is decomposed, producing gases and vapors rich in carbon and hydrogen, and which rise around the wick, forming an irregular cone. The gaseous products consti- tuting this cone do not present the same composition through- out. They have been analyzed by H. Sainte-Claire Deville, by the aid of very ingenious processes. The obscure cone is formed of gaseous products holding in suspension finely-divided carbon, which has not yet arrived at incandescence. These products become heated on reaching the more central portions of the flame. Then the carbon, which is set free by the decomposition of gases rich in carbon, is brought to bright incandescence, but it is completely burned only when it reaches the exterior envelope, where the oxygen is in excess. A simple STRUCTURE OF FLAME. 221 experiment will demonstrate that the most luminous portion of the flame holds in suspension finely-divided and incandes- cent carbon. If a porcelain saucer be depressed into this portion, the carbon will be deposited on the vessel in the form of soot. It is this solid and incandescent carbon which causes the luminosity of the flame. The flame of hydrogen, which con- tains only gaseous products, is pale. In the calcium or Drum- mond light it produces great brilliancy because a solid body, lime, is heated to bright incandescence. When the carbon suspended in a flame is in excess in proportion to the supply of oxygen, it is incompletely burned, and is carried into the air. The flame then smokes. At the base of the cone, carbon monoxide and methane, the first products of the decomposition of the candle, burn on con- tact with the air at dd' with a bluish flame. According to recent experiments, the density of a burning gas is not without influence upon the lustre of the flame. The flame of hydrogen is luminous when that gas is burned under strong pressure (Frankland). Illuminating gas is a mixture of hydrogen with various gas- eous hydrocarbons and a small proportion of carbon monoxide. It is manufactured by the destructive dis- tillation of bituminous coal. The aqueous products containing ammonia, and the tarry matters formed during the distilla- tion are condensed, and the gas is purified by washing with water and passage over slaked lime to remove sulphur and other impurities. Illuminating gas forms an explosive mixture with air, but if the mixture be burned as it is formed, the resulting flame will be almost colorless and will deposit no soot, the whole of the carbon coming in contact with sufficient oxygen for its complete combustion. These conditions are fulfilled in the Bunsen burner (Fig. 89). In this burner, the force of the escaping gas-jet draws in air through holes immediately oppo- site the jet in a wider tube, at the end of which the mixture is burned. 19* Fio. 89. 222 ELEMENTS OF MODERN CHEMISTRY. GENERAL NOTIONS UPON THE METALLOIDS. THEORY OF ATOMICITY. From a consideration of the facts acquired in the study of the elements known as metalloids, we may deduce certain gen- eral consequences, and while looking back on the field over which we have passed, we may at the same time fix certain landmarks for the remainder of our course. The elements which we have studied are not alike in their aptitude to enter into combination, nor in the general characters of their compounds. In this respect, analogies and differ- ences have been established between them, and these have become the basis of a rational classification. Following the example of Dumas, we have arranged these elements in groups or families, uniting in the same group those which are related by their chemical functions. For this reason boron has been separated from silicon and carbon, since it differs from them so far as concerns the composition of their compounds. The groups thus formed are as follows : HYDROGEN. OXYGEN. NITROGEN. BORON. SILICON. SULPHUR. PHOSPHORUS. CARBON. FLUORINE. SELENIUM. ARSENIC. CHLORINE. TELLURIUM. ANTIMONY. BROMINE. IODINE. In order to account for the chemical functions of all these bodies, that is, for the parts which they play in their combina- tions, we must first consider their hydrogen compounds. They constitute the following series : HH H 2 H 3 N H 4 Si Hydrogen. Water. Ammonia. Hydrogen silicide. HC1 H 2 S H 3 P H 4 C Hydrochloric acid. Hydrogen sulphide. Hydrogen phosphide. Hydrogen carbide. HBr H 2 Se H 3 As Hydrobromic Hydrogen Hydrogen arsenide. acid. seleuide. HI H 2 Te H 3 Sb Hydriodic acid. Hydrogen Hydrogen antimonide. telluride. HF1 Hydrofluoric acid. THEORY OF ATOMICITY. 223 It is seen that the preceding groups are characterized by the composition of their hydrogen compounds. While the bodies of the first group combine with hydrogen atom for atom, those of the second group require two atoms of hydrogen, those of the third three, and those of the fourth four, to form hydrogen compounds. Hence we may draw the conclusion that the atoms of these metalloids are far from being equivalent in their power of combination with hydrogen. The atoms of chlorine, bromine, and iodine are equivalent to each other in this respect, for each requires but one atom of hydrogen. The atoms of oxygen, sulphur, etc., are equivalent to each other, for each combines with two atoms of hydrogen. The atoms of nitrogen, phosphorus, arsenic, and antimony are equivalent to each other, for each of them unites with three atoms of hydrogen. Lastly, the atoms of carbon and silicon are equivalent, for each can unite with four atoms of hydrogen. But, on the other hand, it is evident that the atoms of chlo- rine, oxygen, nitrogen and carbon are not equivalent to each other, as regards their power of combination with hydrogen, since each of them unites with a different number of atoms of that body. In this respect it may be said that 1 atom of chlorine is equivalent to 1 atom of hydrogen. 1 atom of oxygen " 2 atoms " 1 atom of nitrogen " 3 atoms " 1 atom of carbon " 4 atoms " It is evident that the capacity of combination which resides in the atoms of simple bodies and by which they attract the atoms of hydrogen, is unequal. Leaving aside its intensity, this force is exerted in different degrees, for it determines the union of 1 atom of chlorine, oxygen, nitrogen, or carbon, with 1, 2, 3, or 4 atoms of hydrogen. This number of hydrogen atoms is the measure of the degree of force which resides in the atoms, of the capacity of combi- nation which they possess for each other. Hence we conclude that The atoms of chlorine and its associates are monatomic or univalent. The atoms of oxygen " " diatomic or bivalent. The atoms of nitrogen " " triatomic or trivalent. The atoms of carbon " " tetratomic or quadrivalent. 224 ELEMENTS OF MODERN CHEMISTRY. The capacity of combination which resides in the atoms, and which is exerted in such different manners according to the nature of the atoms, is called atomicity. Atomicity is the relative equivalence of the atoms ; it is simple or multiple, and if we consider it in its first degree, we may say that the atoms of chlorine and the atoms of hydrogen are so constituted that a single atom of one attracts a single atom of the other. When they combine, they exchange in some manner a unit of satura- tion, and in the combination of chlorine and hydrogen two of these units of force are neutralized ; two units of saturation or two atomicities are exchanged: the atoms of chlorine and of hydrogen are univalent. The force which resides in an atom of oxygen is more com- plex. It attracts two atoms of hydrogen, and represents the second degree of capacity of combination, and we may say that in each atom of oxygen reside two atomicities, which are satis- fied and exchanged when this atom combines with two atoms of hydrogen. Hence, four atomicities are satisfied by the com- bination. Following the same reasoning, we consider that a triple capa- city of combination is active in an atom of nitrogen when this atom unites with three atoms of hydrogen ; and that six atom- icities are satisfied by the combination. Lastly, tetratomic carbon is provided with four atomicities, which are satisfied by the four atomicities which reside in four atoms of hydrogen. If this neutralization or exchange of two units of saturation be represented by a hyphen, we will have the following formulae : H-C1 H-O-H H H Hydrochloric acid. Water. I I N H-C-H /\ i H H H Ammonia. Hydrogen monocarbide. It is seen that in the formulae for water, ammonia and hydro- gen monocarbide, the polyatomic elements, oxygen, nitrogen and carbon, constitute, as it were, the nuclei around which the other atoms are symmetrically grouped. A great many other bodies present the same constitutions as the preceding ; it is evident that a given element in any com- pound may be replaced by another element having the same atomicity, without disturbing the equilibrium of the atomicities. THEORY OF ATOMICITY. 225 Indeed, if we suppose the chlorine, oxygen, nitrogen, and carbon to be replaced by elements of corresponding atomicities, we will have the series of hydrogen compounds already con- sidered. All of the bodies which are classed together in the series belong to the same type. Each contains an equal num- ber of atomicities for the same number of atoms. According to the principle of substitution announced above, it is evident that the hydrogen in each of the hydrogen com- pounds under consideration may be replaced by another mon- atomic element, and the compounds thus formed will still belong to the primitive types. So considered, a great number of compounds possess the same constitution, that is, the same molecular structure, as hydrochloric acid, water, ammonia, and methane or hydro- gen monocarbide. Such are those arranged in vertical columns in the following table : TTPEHCI TYPEII20 TYPE NH3 TYPE H* C1-C1 H-O-H K Cl Free chlorine. Water. I I N C1-C-C1 /\ I H H Cl Potassium amide. Carbon tetrachloride. K-C1 C1-0-C1 Cl Cl Potassium chloride. Hypochlorous oxide. I I P Cl-Si-Cl /\ i Cl Cl Cl Phosphorus trichloride. Silicon tetrachloride. K-I H-O-K Cl H Potassium iodide. Potassium hydrate. I I Sb H-Si-H Ag-I Ag-O-Ag Cl^Cl H Silver iodide. Silver oxide. Antimony trichloride. Hydrogen sillcide. All of these bodies belong to the respective types HC1, H 2 O, NH 3 , CH*, the first three of which were established by Ger- hardt, and have their existence explained by the atomicity of the elements ; that is, by the varying equivalence of their atoms, measured, in the present examples, by the number of hydrogen atoms with which they combine. One atom of oxygen is equivalent to two atoms of hydrogen K* 226 ELEMENTS OP MODERN CHEMISTRY. or two atoms of chlorine. Hence, in the preceding combina- tions, two atoms of chlorine may be replaced by one atom of oxygen without changing the equilibrium of the atomicities. Thus, the oxides SiO 2 ,C0 2 , correspond to the chlorides SiCl 4 , CC1 4 , and belong to the same type. The four atomicities of an atom of silicon or carbon are saturated by the four atomici- ties of two atoms of oxygen. The trichlorides of phosphorus and antimony, PCI 3 and SbCP, which will be found in the preceding table, require an impor- tant remark. They are not saturated with chlorine, and each may combine with two more atoms of that element, producing the compounds PCI 5 and SbCl 5 . Thus, while phosphorus exhausts its power of combination with hydrogen in uniting with three atoms of that element in PH 3 , its capacity of combination with chlorine is only exhausted when it has combined with five atoms ; while it plays the part of a triatoniic element in hydrogen phosphide, it is pentatomic in phosphorus pentachloride. From these facts it follows that it is often difficult to meas- ure in an absolute manner the capacity of combination which resides in an atom; for that capacity varies according to the nature of the elements upon which it is exerted. Affinity is an elective force. A given element does not attract all of the other elements with equal facility ; it selects certain ones by preference, and neglects the others. With one, it may form but a single compound ; with another, it may form several. Nitrogen forms with hydrogen but one combination, ammo- nia, NH J , which cannot fix any more atoms of hydrogen. Sat- urated with hydrogen in ammonia, nitrogen manifests in con- tact with that element but three atomicities. But let ammonia be brought in contact with a body other than hydrogen, hydro- chloric acid, for example, and it will combine with it, forming ammonia hydrochloride, or ammonium chloride. If its ca- pacity of combination is exhausted for hydrogen, HH, it is not exhausted for hydrogen combined with chlorine, HC1. Thus, an atom of nitrogen possesses other affinities than those which it manifests for hydrogen in ammonia. While nitrogen is triatomic in ammonia because it is united with three mon- atomic atoms, it behaves as a pentatomic element in ammonium chloride. The parts which polyatomic elements play in their compounds may be expressed by accents marking the number of atomici- THEORY OF ATOMICITY. 227 ties or the quantivalence of the element, as shown in the following formulae : 0"H 2 N'"H 3 N V H 4 C1 P"CP P V C1 5 C iv O" 2 Water. Ammonia. Ammonium Phosphorus Phosphorus Carbon chloride. trichloride, pentachloride. dioxide. In these compounds, as has been remarked before, the poly- atomic elements form, as it were, the nuclei around which the other elements are grouped. This is an important idea, since it leads to the determination of the constitution of the mole- cules, that is, the arrangement of their atoms. The considera- tions just presented concerning the functions of the elements in compounds alone permit the resolution of this question ; they alone lead to the discovery of the relations existing be- tween the atoms in their combinations, and to the determina- tion of their relative positions, in a word, to the revelation of the molecular structure. The following developments will demonstrate this fact. We will reconsider certain of the combinations above men- tioned, which have been taken as types. In water, an atom of diatomic oxygen fixes two atoms of hydrogen. One atom of oxygen can fix two atoms of any monatomic element, forming compounds belonging to the same type as water ; but it cannot at the same time fix a monatomic element and a diatomic element. In other words, an atom of hydrogen in water may be replaced by an atom of chlorine, bromine, iodine, or potassium, but not by an atom of oxygen ; and if a second atom of the latter element be joined to the oxygen of water, it will be seen that there remains a free affin- ity which may be satisfied by hydrogen. Hydrogen dioxide would result. H-0"-H H-0"-0"-H Water. Hydrogen dioxide. Hence, we draw the conclusion that in hydrogen peroxide, the two atoms of oxygen are combined with each other, and that in uniting together each atom loses one atomicity, the two others being satisfied by hydrogen. The same considerations are applicable to the compounds of chlorine and oxygen. Hypochlorous acid may be regarded as composed of an atom of chlorine united to the group hydroxyl. d-0"-H = Cl(OH)' Hypochlorous acid. 228 ELEMENTS OP MODERN CHEMISTRY. In this compound the chlorine exchanges one unit of satu- ration with the oxygen of the group OH, just as it exchanges one with hydrogen in hydrochloric acid: it is monatomie or univalent. In chloric acid it is combined with two atoms of oxygen and one group, OH. It exchanges 4 atomicities with oxygen, arid one with the group OH : C1 V 0" 2 (OH)' Cbloric acid. Chlorine thus manifests 5 atomicities in chloric acid ; but it has 7 in perchloric acid. Cl vii 3 (OH)' Perchloric acid. Without dwelling on these considerations, we will take one more example. In hydrogen phosphide, one atom of phosphorus is combined with three atoms of hydrogen ; it manifests but three atomici- ties, and these could not neutralize those which reside in three atoms of oxygen, since the latter possess six atomicities. If, then, three atoms of diatomic oxygen were united with one atom of triatomic phosphorus, it is clear that three affinities would remain free, one in each of the three atoms of oxygen. In phosphorous acid, these three affinities of the oxygen atoms are satisfied by three atoms of hydrogen. We may suppose that in the molecule of this compound, the phosphorus is the nucleus around which are grouped three atoms of oxygen, each of which is joined also to one atom of hydrogen. This atomic grouping is indicated in the following formulae : H OH i i P P H /X H HO OH Hydrogen phosphide. Phosphorous acid. This hydrogen, combined with the oxygen in all of the oxy- gen acids, plays invariably the same part: it saturates the one atomicity which remains free in one atom of oxygen. The oxygen thus combined with an atom of hydrogen, has lost one of its atomicities by the fact of this combination ; it still retains one in the group OH, which represents, as it were, water less one atom of hydrogen. HOH H = (OH)' THEORY OF ATOMICITY. 229 This group is named hydroxyl, and it is evident that, although it cannot exist by itself, it may play the part of a monatomic element, for it retains one free atomicity. It may then replace a monatomic element, such as hydrogen or chlo- rine. Indeed, it plays an important part in the constitution of acids. If we consider the examples which have already been dis- cussed, we will notice that it is this hydroxyl which, by com- bining with an element or group of elements capable of forming acids, confers upon them the characters of acids. So consid- ered, hypochlorous acid is formed by the union of hydroxyl with an atom of chlorine. Cl(OH)' Hypochlorous acid. Sulphuric acid is formed by the union of two hydroxyl groups with sulphurous oxide, and represents in a manner sulphuryl chloride in which the two atoms of chlorine are replaced by two hydroxyl groups. C1 SO 2 1 (OH )' Cl b { (OH/ Sulphuryl chloride. Sulphuric acid. Phosphorous acid is formed by the union of three hydroxyl groups with one atom of phosphorus. Cl (OH)' Cl (OH)' Phosphorus trichloride. Phosphorous acid. Lastly, phosphoric acid results from the union of three hy- droxyl groups with one atom of phosphorus already combined with one atom of oxygen (phosphoryl). Cl ( (OH)' Cl O'TM (OH)' Cl ((OH)' Phosphoryl trichloride. Phosphoric acid. Such, according to the theory of atomicity, are the relations existing between the atoms of certain acids ; such, in other words, is the constitution of these acids. It would be easy to extend these considerations to other bodies, but the examples we have chosen are sufficient to indicate the importance of the idea of atomicity, when it is applied to the discovery and definition of 20 ( 230 ELEMENTS OF MODERN CHEMISTRY. the part played by each element in a given compound. By supposing the capacities of combination of chlorine, oxygen, sulphur, and phosphorus to be known, we have been able to follow these bodies in their most important combinations, we have seen how they attract and group around themselves other elements. We have thus been able to penetrate the atomic structure of the molecules, and have built up as it were the molecular edifice. It must be remembered, however, that the preceding formulae do not in any manner represent the real positions of the atoms in space. Their sole object is to indi- cate the points of attachment of the affinities, and consequently the mutual relations between the atoms. METALS. THE metals are elements which are good conductors of heat and electricity, and are endowed with a peculiar lustre, which is called the metallic lustre. This definition, it will be ob- served, is founded upon certain physical characters rather than upon chemical properties. It is unsatisfactory and wanting in exactness, for it is applicable to bodies which are properly con- sidered as metalloids. Such is antimony, which has already been described, and bismuth, which should be placed beside antimony. Indeed, the distinction between the metals and metalloids is not so well marked that a line which shall sepa- rate these two classes of simple bodies may be sharply drawn. Physical Properties of the Metals. These will be found in the table on page 232, but the indications there given may be completed by certain other developments. The metals are opaque, but their opacity is not absolute. A sheet of gold-leaf pressed out between two plates of glass allows the passage of a green light. Gold possesses a brilliant lustre and a yellow color, but it loses this lustre when it is reduced to a minute powder. When, however, this powder is rubbed with a hard body, when, for example, it is triturated in an agate mortar, or passed under the burnisher, it acquires a certain degree of cohesion, and again assumes its lustre. It is thus with all the metals. They lose their metallic lustre when finely divided and reassume it on burnishing. The yellow color of gold is not its true color ; the rays which reach the eye are the result of but one reflection, but if light be successively reflected from ten surfaces of gold, the metal will appear of a bright-red color. Under the same circum- stances, copper will appear scarlet, zinc indigo, iron violet, and silver pure yellow (B. Prevost). Most of the metals may be crystallized. Bismuth is the most striking example. If a few kilogrammes of pure bismuth be fused, and the liquid mass be allowed to cool slowly, the 231 232 ELEMENTS OF MODERN CHEMISTRY. by the nail. oft at ordinary temperatures. s a So s.::: : f *i If* ::i| ; * If l linn!* i I! n OH^OCDOQPSOH ^4 c-. x> S I : -J 'bl| : jr ; l S J3 illii S SS !! a 1 S ll 1 [iflfllllllJ! (Swoi IISs</ y gen and an atom of a monatomic metal, TT > SO 4 . 2. It is united with two atoms of a monatomic metal in the neutral sulphates E/ 2 S0 4 . 3. With one atom of a diatomic metal in the neutral sul- phates M"S0 4 . These cases are very simple. It is not so, however, with M* 274 ELEMENTS OP MODERN CHEMISTRY. the fourth, in which we consider the saturation of sulphuric acid by an oxide I1 2 3 , such as ferric oxide or aluminic oxide. Each of the three atoms of oxygen of the oxide R 2 3 removes H 2 from a molecule of H 2 S0 4 , and it results that the metal which was combined with 30", combines with 3(S0 4 )". The two atoms of metal which are substituted for 3H 2 in three mol- ecules of H 2 SO* are then equivalent to 6 atoms of hydrogen. They are hexatomic, as is marked by the index vi . Properties. The sulphates are nearly all soluble in water. Those of barium, strontium, and lead are insoluble. The sul- phates of calcium and silver, and mercurous sulphate are but slightly soluble. The alkaline sulphates, and those of calcium, barium, stron- tium, magnesium, and lead, are undecomposable by heat. The others are decomposed at a high temperature. A residue of oxide generally remains, while sulphurous oxide and oxygen are disengaged. The sulphates of zinc and copper are thus decomposed at a high red heat. CuSO 4 = SO 2 + + CuO Cupric sulphate. Cupric oxide. In case the oxide is reducible by heat, the residue consists of metal. HgSO = Hg + SO 2 + O 2 Mercuric sulphate. Mercury. The sulphates R 2 (S0 4 ) 3 are decomposed at a comparatively low temperature, disengaging vapor of sulphur trioxide and leaving a residue of sesquioxide. Fe 2 (SO*) 3 = Fe 2 3 -f 3S0 3 Ferric sulphate. Ferric oxide. Sulphuric oxide. The sulphates are easily reduced by bodies avid of oxygen, such as charcoal. If an intimate mixture of potassium sulphate with an excess of charcoal be heated to bright redness, and allowed to cool out of contact with the air, a black powder is obtained, which pro- duces a shower of sparks when projected into the air. It is the pyrophorous of Gray-Lussac. It owes its spontaneous in- flammability on contact with the air to finely-divided potassium sulphide which it contains, and which attracts oxygen with great avidity. The sulphide is formed according to the following reaction : K 2 S0 4 + 40 = 4CO +' K 2 S Potassium sulphate. Potassium sulphide. CARBONATES. 2*75 In the same manner barium sulphate and calcium sulphate are converted into sulphides by the action of charcoal at a high temperature. The other sulphates are also reduced under the same circum- stances, but the products vary; carbon dioxide or carbon mon- oxide and sulphurous oxide are disengaged, and the residue consists of either oxide or metal. Distinctive Characters. When treated by sulphuric acid, the sulphates do not evolve any gas. They do not deflagrate when thrown upon burning charcoal. Their solutions give a white precipitate of barium sulphate with barium nitrate, which is insoluble in nitric acid. When this precipitate is washed, dried, and calcined with an excess of charcoal, it leaves a resi- due of barium sulphide, and when this is moistened with hy- drochloric acid, it evolves hydrogen sulphide, which is easily recognized by its odor. CARBONATES. Composition. Carbonic acid is dibasic, like sulphuric acid. It is not known in the state of hydrate, and the carbonates are formed by the direct union of carbon dioxide with the metallic oxides or hydrates. When freshly-burnt lime is exposed to the air, it attracts at the same time the moisture and the carbonic acid gas of the air, and is converted into carbonate. CO 2 -f CaO = CaCO 3 Calcium oxide. Calcium carbonate. The carbonates then contain the group CO 3 combined with a metal. In carbonic acid, this group would be united with two atoms of hydrogen. The composition of the more simple car- bonates is expressed by the following formulae: H 2 C0 3 carbonic acid (unknown). R' ) TT [ CO 3 acid carbonates (dicarbonates). R' 2 C0 3 neutral carbonates. M"C0 3 neutral carbonates. In these formulae, R/ represents a monatomic metal, such as potassium, which is equivalent to one atom of hydrogen. M" represents a diatomic metal, such as calcium, which is equiva- lent to two atoms of hydrogen. Properties. Only the alkaline carbonates are soluble in pure 276 ELEMENTS OF MODERN CHEMISTRY. water. The others are insoluble, but they dissolve in water charged with carbonic acid. The soluble carbonates possess an alkaline reaction. It is the same with the acid carbonates of the alkaline metals, which are ordinarily called bicarbonates, such as potassium dicarbonate KHCO 3 . All of the carbonates except the alkaline carbonates are de- composable by heat. In this decomposition carbon dioxide is disengaged, and there remains a residue of oxide, or of metal in case the oxide be reducible by heat. Thus, the carbonates of magnesium, calcium, zinc, lead, and copper leave a residue of oxide after calcination ; silver carbonate leaves a residue of metal. Barium carbonate is but slowly decomposed at a white heat ; its decomposition is facilitated by heating it in a current of steam. Bodies avid of oxygen act upon the carbonates as upon the oxides ; the metal is reduced if the base be reducible. Char- coal acts in this manner upon the carbonates. If cupric carbonate be heated with charcoal, carbon dioxide is disengaged, and metallic copper remains. 2CuC0 3 + C = SCO 2 -f 2Cu Cupric carbonate. Copper. In this experiment carbon dioxide is disengaged, for cupric oxide is easily reducible by charcoal. It is not the same with potassium oxide ; hence potassium carbonate is only reduced by charcoal at a very high temperature with disengagement of carbon monoxide. K 2 C0 3 + 20 = 3CO -f K 2 When barium carbonate is heated with charcoal, carbon monoxide is disengaged in the same manner, but there remains a residue of barium oxide, for the latter is irreducible by char- coal. BaCO 3 + C = 2CO -f BaO Phosphorus decomposes all of the carbonates. A small piece of phosphorus may be placed at the bottom of a small test-tube, and the latter then nearly filled with well- dried sodium carbonate. The part of the tube containing the carbonate being heated to redness, the phosphorus may be heated so that its vapor will pass over the incandescent car- CLASSIFICATION OF THE METALS. 277 bonate. The latter will be decomposed with the formation of sodium phosphate and a deposition of carbon. After cooling, the contents of the tube will be black. The experiment may be repeated upon calcium carbonate. The phosphorus is placed in a small crucible, which is then introduced into a larger one. The calcium carbonate (chalk) is then placed upon the lid of the smaller crucible, which is pierced with holes. The arrangement is heated upon a double grate, so that when the chalk has been brought to incandes- cence, the vapor of phosphorus may be caused to pass through it by placing some hot coals upon the lower grate. The chalk is rapidly decomposed, carbon monoxide is disengaged, and a mixture of calcium phosphate and phosphide is formed. This mixture serves for the preparation of hydrogen phosphide. Distinctive Characters. When treated with sulphuric acid, the carbonates disengage a cblorless, incombustible gas, which extinguishes burning bodies and produces a milkiness when agitated with lime-water. CLASSIFICATION OF THE METALS. In the preceding pages we have studied the composition and the general properties of metallic compounds. This study has revealed the fact that the metals possess very different aptitudes to form compounds, and various capacities of combination, which are manifested by the greater or less number of other atoms which the atoms of these metals can attract. In this respect, the differences existing between the metals are analogous to those which we have already remarked between the metalloids. On comparing the metals among themselves, some are discov- ered which resemble each other in the general structure of the compounds which they are capable of forming, and such can naturally be classed in the same group. On this plan the metals are divided into several families analogous to those first proposed by Dumas for the metalloids, and it will be seen that the general composition of the metallic compounds furnishes the elements for a natural classification of the metals. While this principle is excellent, its application is attended with some difficulties which chemistry has not yet been able to solve. Consequently, this chapter must be limited to summary indi- cations upon the subject. Some of the metals are incapable of combining with more 24 278 ELEMENTS OF MODERN CHEMISTRY. than a single atom of chlorine, bromine, or iodine. The com- pounds thus formed correspond in their atomic constitution to hydrochloric, hydriodic, and hydrobromic acids. On comparing potassium chloride or silver chloride to hydrochloric acid, it will be seen that an atom of potassium or an atom of silver occupies in them the place occupied by the hydrogen of the acid. The atoms of potassium and of silver are therefore equivalent to the atoms of hydrogen as far as their capacity of combination is concerned. The other alkaline metals, such as sodium and lithium, are similar and belong to the same group. Their chlorides, bromides, and iodides, which are arranged in the following table, present analogous compositions : MONATOMIC METALS. MONATOMIC CHLORIDES. MONATOMIC BROMIDES. MONATOMIC IODIDES. H'Cl P,Br Ill Potassium K' Sodium Na' KC1 NaCl KBr NaBr KI Nal LiCl LiBr Lil Silver Ag' AgCl AgBr Agl These metals form oxides whose atomic constitutions corre- spond to that of water, ea'ch containing two atoms of metal for one of oxygen. Their sulphides correspond to hydrogen sul- phide, containing two atoms of metal for one of sulphur. "With the oxides and sulphides we may group the hydrates and sulphydrates, which possess analogous atomic constitutions. TYPE H20. TYPE H2S. OXIDES. HYDRATES. MONOSIJLPHIDES. SULPHYDRATES. K"0 KOH K2S KSH Na 2 NaOH Na 2 S NaSII Ag0 Ag'S The same analogy is continued between the salts of these metals, as will be seen from the nitrates and sulphates which we take as examples. NITRIC ACID, HNO 3 . SULPHURIC ACID, IPSO 4 . NITRATES. KNO S SULPHATES. Na 2 SO* ACID SULPHATES. KHSO* NaHSO* AgNO CLASSIFICATION OP THE METALS. 279 It is seen that in all of these compounds the metals under consideration replace hydrogen atom for atom ; each of them possesses the same capacity of combination as that gas. They are said to be monatomic. Certain other metals manifest a double capacity of combina- tion; one atom of any of these is capable of replacing two atoms of hydrogen, consequently it can combine with two atoms of chlorine, bromine, or iodine, or with one atom of oxygen or sulphur. In the chlorides of these metals, the two atomicities of the metal are satisfied by the two atomicities of two atoms of chlorine. In their oxides, the two atomicities of the metal are satisfied by the two atomicities or bonds of affinity which reside in one atom of oxygen. These metals are then diatomic. They are quite numerous and can be divided into several groups, one of the most natural of which com- prises barium, strontium, calcium, and lead. The following table shows the constitution of the principal compounds of these metals : DIATOMIC METALS. CHLORIDES. OXIDES. NITRATES. SULPHATES. 2HC1 H 2 2HN0 3 II 2 SO* Barium Ba" . Bad 2 BaO Ba(N0 3 ) 2 BaSO* Strontium Sr" . SrCl 2 SrO Sr(N0 3 ) 2 SrSO* Calcium Ca" . CaCl 2 CaO Ca(N0 3 ) 2 CaSO* Lead Pb" . . PbCl 2 PbO Pb(N0 3 ) 2 PbSO* The metals of this group combine with oxygen in two pro- portions, forming not only the monoxides, RO, but also the dioxides, RO 2 . They thus form two oxides, while they are capable of forming but one chloride, RCP. Thus, barium forms a monoxide, BaO, a dioxide : BaO 2 , and a dichloride, BaCl 2 ; but no tetrachloride of barium is known, and it is not probable that barium can act as a tetratomic element. How is it, then, that in the dioxide this metal can combine, with two atoms of oxygen, while it cannot combine with four atoms of chlorine, which are equivalent to two atoms of oxygen ? In other words, what is the atomicity of barium in the dioxide which would seem to correspond to a tetrachloride ? It is 280 ELEMENTS OP MODERN CHEMISTRY. undoubtedly diatomic in the dioxide as it is in the monoxide, and the constitution of barium dioxide is analogous to that of hydrogen dioxide, which has already been indicated. The two atoms of oxygen mutually satisfy two of their atomicities by combining together, and they retain two which are neutral- ized in combining with the diatomic atom of barium. Thus, in barium monoxide one atom of oxygen is joined to one atom of barium by both of its atomicities ; in the dioxide two atoms of oxygen are united to one atom of barium, each by one atom- icity. If we represent the saturation of two atomicities by a straight line, as has before been explained, we will have the following formulae : Ba^O Ba Barium iuonoxLk\ /\ 0-0 Barium dioxide. In this manner, theory enables us to fix the relations existing between the atoms in a given body. The comparison may be continued between the other diatomic metals. Magnesium, the radical of magnesia, somewhat resem- bles calcium in its relations, and forms, as it were, the centre of a group including magnesium, zinc, cobalt, and nickel, and which is called the magnesium group. Manganese and iron, on one hand, and copper, on the other, seem to join this group by certain of their characteristics. In their most stable and gen- erally their most important compounds, these metals act as diatomic elements. All form the dichlorides RC1 2 and the oxides RO. But in other compounds, manganese and iron seem removed from the metals of this group, and resemble chromium and aluminium. Copper, which resembles magne- sium in the series of cupric compounds, approaches mercury in the cuprous series. Bismuth, which might be classed with antimony, and gold are triatomic in their most important combinations. They form the chlorides BiCl 3 and AuCP. A certain number of the metals may be. grouped together as tetratomic, since they manifest four atomicities in their principal combinations. They are tin, titanium, and zirconium. They form the chlorides RC1* and the oxides RO 2 . In stannic chlo- ride, SnCl 4 , the tin is saturated with chlorine, of which it cannot combine with more than four atoms; it is tetratomic in this saturated compound. But it may combine with only CLASSIFICATION OF THE METALS. 281 two atoms of chlorine, thus forming the chloride SnCl 2 , which is not saturated, for it can still fix two more atoms of chlorine. Tin only manifests two atomicities in the dichloride. In the same manner, ferrous chloride, Fed 2 , can absorb chlorine, becoming ferric chloride. The latter contains two atoms of iron and six of chlorine. These two atoms of iron exist in all the ferric compounds ; together they manifest six atomicities, for in ferric chloride they are united with six atoms of chlorine. They constitute a hexatomic couple. COMPOUNDS. CHLORIDES. OXIDES. SULPHATES. Fe 2 Cl 6 Fe 2 3 Fe 2 (S0 4 ) 3 Manganic ...... Mn 2 Cl 6 Mn 2 3 Mn 2 (SO*) 3 Cr 2 Cl 6 Cr 2 3 Cr 2 (S0 4 ) 3 Aliiiniuic . . ... A1 2 C1 6 A1 2 3 A1 2 (S0 4 ) 3 The following table gives a resume of the constitution of the principal metallic combinations. The metals there chosen as examples have different atomicities. The hexatomic couple, consisting of two atoms of iron, may for convenience be called ferricum. METALS. CHLORIDES. OXIDES. NITRATES. SULPHATES. Monatomic metal Potassium K' . KC1 K20 KN03 K2SO* Diatomic metal Barium Ba" . . . BaC12 BaO Ba(N03)2 BaSO* Triatomic metal Bismuth Bi'" . . BiC13 Bi203 Bi(N03)3 Bi2(SO*)S Tetratomic metal Tin Sriiy . . . SnCl* SnO 2 Hexatomic group Ferricum (Fe2)vi Fe2C16 Fe20 3 Fe2(N03,6 Fe2(SO*)3 Such are the principles furnished by the theory of atomicity for a rational classification of the metals. 24* 282 ELEMENTS OF MODERN CHEMISTRY. POTASSIUM. K = 39.1. Potassium was discovered by Sir Humphry Davy in 1807. It ordinarily occurs in commerce in gray, globular masses, readily yielding to the pressure of the nail. It has a dull, tarnished appearance, but when freshly cut it exposes a brilliant surface. It is the metallic radical of potash. If a fragment of this metal be thrown into water, it at once takes fire and rushes about on the surface of the liquid, burn- ing with a violet flame. Finally, it disappears with a little explosion. This brilliant phenomenon is due to the energy with which potassium decomposes water. 2H 2 + K 2 = 2KOH + H 2 The hydrogen which is disengaged is inflamed by the incan- descent metal. The potassium hydrate formed ultimately dis- solves in the water, but its temperature being very high at the moment of its solution, and its combination with the water also producing heat, there results a sudden formation of steam, which gives rise to the little explosion. Preparation and Properties. Potassium is prepared by decomposing potassium carbonate by carbon at a high tempera- ture. K 2 C0 3 + 20 = SCO + K 2 Potassium carbonate. Carbon monoxide. The mixture is heated to whiteness in an iron retort and the vapors are passed into a copper receiver. The potassium dis- tils and condenses in globules or irregular masses, still contain- ing charcoal and a black substance. It is purified by redistilla- tion in an iron retort, and is condensed in a copper receiver filled with naphtha. The manufacture of potassium is a dan- gerous operation. It is accompanied by the formation of various accessory products, among which is a black substance which sometimes explodes spontaneously on contact with the air. Potassium melts at 62.5 (Bunsen). It boils at a red heat, and its vapor is green. When exposed to the air, it rapidly absorbs oxygen and at the same time decomposes the atmos- pheric moisture. It inflames at a temperature but slightly elevated and becomes converted into oxide. POTASSIUM OXIDES. POTASSIUM HYDRATE. 283 POTASSIUM OXIDES. Potassium monoxide, K 2 0, is formed when thin pieces of the metal are abandoned to the action of dry air, or when potassium hydrate is heated with potassium. 2KOH + K 2 = 2K 2 + H 2 It is a grayish- white substance which unites with water with extreme violence, forming potassium hydrate. K 2 + H 2 = 2KOH A tetroxide of potassium, K 2 4 , is formed when potassium is heated in an excess of oxygen, but it is little known. POTASSIUM HYDRATE, OR CAUSTIC POTASSA. KOH This important compound is prepared by boiling 1 part of potassium carbonate with 12 parts of water, and gradually add- ing milk of lime to the boiling liquid. The lime combines with the carbonic acid forming an insoluble carbonate, while the potassa remains in solution. K 2 C0 3 -f Ca(OH) 2 = CaCO 3 + 2KOH Calcium hydrate. Calcium carbonate. When the decomposition is finished the liquid is allowed to settle, and the clear solution decanted and rapidly evaporated. FIG. 97. The residue is melted in a silver dish and poured out upon flat stone slabs or cast in cylindrical metallic moulds (Fig. 9*7). This product is known as potash by lime. It is impure. By treating it with alcohol, which dissolves only the potassium 284 ELEMENTS OF MODERN CHEMISTRY. hydrate, it may be purified from lime, and the salts of potas- sium it may contain, and especially the carbonate, which is formed by the absorption of carbonic acid gas from the air during the evaporation. The clear alcoholic solution is decanted, and after the alcohol has been expelled by distillation, the resi- due is evaporated to dryness and fused in a silver dish. It is known as potash by alcohol. Recently-fused potassium hydrate occurs as opaque, white fragments having a short fibrous fracture and a density of 2.1. It melts at a red heat and volatilizes at whiteness ; it is not decomposed by heat. When exposed to the air, it absorbs moist- ure and carbonic acid gas, and deliquesces. It is very soluble in water, and produces heat in dissolving. A hydrate, KOH -j- 2H 2 0, is deposited from its hot and very concentrated solu- tion in acute rhombohedra. Potassium hydrate is decomposed by iron at a white heat : oxide of iron is formed, and hydrogen and potassium vapor are disengaged. Gay-Lussac and Thenard founded a process for the preparation of potassium on this decomposition. Until then the metal had only been obtained in small quantities by Davy by the electrolysis of potassium hydrate. Potassium hydrate is very caustic. It softens and destroys the skin, and for this purpose is employed in surgery as a caustic. It manifests the properties of an alkali in the highest degree ; these are its solubility in water, its power to neutralize the acids and decompose a great number of metallic solutions, and its corrosive action on the tissues. This alkalinity may be shown by the energy with which the most feeble solutions of potassa restore the blue color to reddened litmus, and change to green the tincture of violets. SULPHIDES OF POTASSIUM. Potassium will burn in vapor of sulphur. It unites with the latter body in five different proportions, forming the sul- phides K 2 S, K'S 2 , K 2 S 3 , K 2 S 4 , and K 2 S 5 . Potassium monosulphide is formed when potassium sulphate is heated to redness in a current of hydrogen, or in a brasqued 1 and covered crucible with charcoal. 1 A brasqued crucible is a clay crucible into which powdered charcoal moistened with gum-water has been strongly pressed, and afterwards cal- cined. The substance to be reduced is placed in a cavity hollowed out in the charcoal. POTASSIUM CHLORIDE. POTASSIUM IODIDE. 285 K 2 S0 4 + 4C = 4CO + K 2 S Potassium sulphate. Potassium monosulphide. A reddish, deliquescent, and caustic mass is thus obtained. When a mixture of sulphur and potassium carbonate is fused, carbon dioxide is disengaged, and a brown mass is obtained on cooling, which is known as liver of sulphur. It is a mixture of potassium polysulphide with undecomposed carbonate and potassium sulphate or hyposulphite, according to the tempera- ture and the proportions of sulphur which have been employed. With an excess of sulphur, potassium pentasulphide is obtained. Liver of sulphur dissolves in water with a brown-yellow color. Potassium pentasulphide and hyposulphite are also formed when potassium hydrate is boiled with an excess of flowers of sulphur. The filtered solution is brown. When treated with hydrochloric acid, it evolves hydrogen sulphide, and finely- divided, yellowish, pulverulent sulphur is deposited. K 2 S 5 + 2HC1 = 2KC1 -h H 2 S + S 4 POTASSIUM CHLORIDE. KC1 This salt is found crystallized in cubes in the neighborhood of certain fissures of Vesuvius, and in thin layers in the saline deposits at Stassfurth, Prussia, and in other localities. At Stassfurth there is found a double chloride of potassium and magnesium, KCl,MgCl 2 -f 6H 2 0. When this double salt is dissolved in hot water, the greater part of the potassium chloride is deposited on cooling while the magnesium chloride remains in solution. Potassium chloride crystallizes in cubes, but it sometimes separates in octahedra from solutions containing free potassa. It is unaltered by the air. Its taste is analogous to that of sodium chloride ; it is more soluble in water than the latter, and produces a greater depression of temperature in dissolving. . 1 part of chloride of potassium dissolves in 3 parts of water at 17.5. 100 parts of water at dissolve 29.23 parts of potassium chloride and 0.2738 additional for each degree of temperature. POTASSIUM IODIDE. KI This compound is quite important on account of its use in medicine. It is obtained by adding powdered iodine to solution 236 ELEMENTS OP MODERN CHEMISTRY. of potassium hydrate until the latter is completely neutralized. Potassium iodide and iodate are formed, the latter being pre- cipitated. The whole is evaporated to dryness, and the residue heated to redness, by which the iodate is converted into iodide. The mass is redissolved in boiling water and the solution con- centrated ; fine cubical crystals of potassium iodide are obtained on cooling. These crystals are opaque and anhydrous. They melt at a red heat without decomposition ; their taste is salty and some- what bitter. 100 parts of water at 18 dissolve 143 parts of potassium iodide. A solution of potassium iodide dissolves iodine abundantly, assuming a dark-brown color. If nitric acid be added to a solution of potassium iodide, iodine is at once deposited and red vapors are disengaged if the solution be concentrated (page 131). This decomposition of potassium iodide takes place even in very dilute solutions. It may serve for the detection of the smallest trace of this salt if a solution of starch be previously added to the liquid ; in this case a blue color will be produced. Potassium bromide is prepared by a process similar to that which yields potassium iodide. It crystallizes in cubes which are soluble in about 1.5 parts of cold water. POTASSIUM NITRATE. This important salt, long known as nitre and saltpetre, im- pregnates the soil and sometimes effloresces upon its surface in certain regions of India, Egypt, Persia, Hungary, and Spain. In the United States, it is found in many localities, generally in caverns in limestone rock, called saltpetre caves. It is obtained by lixiviating the earthy matters containing it and evaporating the solution. It is less abundant in northern climates. It is formed wherever nitrogenized organic substances decompose in pres- ence of potassa. Thus, it exists in small quantities in the soil of cellars, in moist walls, and in the debris of demolitions. In these cases it is mixed with a certain quantity of sodium nitrate and a large excess of calcium and magnesium nitrates. Formerly such materials were lixiviated to obtain the nitrates, all of which were then converted into potassium nitrate. Nitre is also manufactured artificially by exposing to the air mixtures POTASSIUM NITRATE. 287 of animal matters with wood-ashes and lime which are fre- quently moistened with stale urine or stable-drainings. How- ever, a great part of the potassium nitrate employed in the arts is now obtained from the natural sodium nitrate of Peru. Two processes are employed. One consists in adding the sodium nitrate to a concentrated boiling solution of potassium carbonate : sodium carbonate being less soluble than the latter, is precipitated and continues to deposit during the concentration ; it is removed, and the potassium nitrate, which is very soluble in hot water, crystal- lizes out on cooling. The second process consists in decomposing the sodium nitrate with potassium chloride. The saturated and boiling mixture of the two solutions deposits sodium chloride, which is sepa- rated, and the potassium nitrate crystallizes on cooling. Properties. This salt crystallizes from its aqueous solution in long, six-sided prisms, terminated by six-sided pyramids. Gen- erally these crystals are grooved or striated. They belong to the right rhombic system. Their taste is cooling and slightly bitter. Potassium nitrate melts at about 350 ; at a higher tem- perature it disengages oxygen and is converted into potassium nitrite, KNO 2 , which is in its turn decomposed at a red heat, leaving a mixture of oxide and peroxide of potassium. Potassium nitrate is very soluble in hot water : 100 parts of water at dissolve only 13.32 parts of the salt, but at 18 they dissolve 29 parts ; at 97, 236 parts ; and at 100, 246 parts. The facility with which potassium nitrate parts with its oxy- gen, of which it contains nearly half its weight, renders it an energetic oxidizer of many bodies. If a small quantity of pulverized saltpetre be thrown upon glowing coals, the salt melts and decomposes, increasing the combustion at the point of contact with the fuel : it is said to deflagrate upon hot coals. The nitrate becomes converted into carbonate. Gunpowder is an intimate mixture of saltpetre, charcoal, and sulphur. As is well known, the combustion of this sub- stance is instantaneous, and gives rise to the sudden formation of gaseous products. The decomposition may be expressed generally by stating that the charcoal combines with the oxy- gen of the nitre to form carbon dioxide and carbon monoxide ; the nitrogen is liberated, and the sulphur combines with the potassium forming potassium sulphide. As the mixture con- 288 ELEMENTS OF MODERN CHEMISTRY. tains all of the oxygen necessary for its own combustion, the latter can be effected in a limited and closed space. It can readily be understood that the explosive energy of the powder is due to a sudden evolution of gas occupying many times the volume of the powder, and of which the volume is still further augmented by the high temperature. POTASSIUM SULPHATE. This salt is obtained as a by-product in various industrial operations. It deposits from the mother-liquors of the soda from sea-weed when these are exposed to low temperatures. It may be made by saturating with potassium carbonate the potas- sium acid sulphate which is formed in the preparation of nitric acid by the decomposition of potassium nitrate with sulphuric acid, a process which is now but little employed. It crystallizes in four-sided prisms or in double, six-sided pyramids belonging to the orthorhombic system. These crys- tals are hard, anhydrous, unaltered by the air, and melt at a red heat without decomposition. They are but slightly soluble in water and insoluble in absolute alcohol. 100 parts of water at dissolve 8.36 parts, and 0.1741 part for each additional degree of heat. POTASSIUM ACID SULPHATE. This salt may be obtained by fusing 13 parts of the neutral sulphate with 8 parts of concentrated sulphuric acid. The saline mass is dissolved in boiling water, and the solution when properly concentrated deposits rhombic octahedra or tabular crystals belonging to the orthorhombic system. Potassium acid sulphate is much more soluble in water than the neutral salt ; its solution is acid. When strongly heated, it first gives up water and then sulphuric oxide, leaving a resi- due of neutral sulphate. POTASSIUM CHLORATE. KC1Q3 This salt is formed, together with potassium chloride, by the action of chlorine upon a concentrated solution of potassium hydrate or carbonate : 6C1 + 6KOH == KC10 3 + 5KC1 + 3H 2 POTASSIUM PERCHLORATE. 289 It is less soluble than the chloride, and is consequently de- posited in great part as the solution becomes saturated with chlorine. It is purified by several recrystallizations. In the arts, it is obtained by the action of chlorine upon a mixture of lime, potassium chloride, and water, heated in closed vessels. Chlorate and chloride of calcium are formed, and in presence of the potassium chloride, a double decomposition takes place, potassium chlorate and calcium chloride, which is very soluble, being formed. The liquid is filtered hot, and the potas- sium chlorate crystallizes out on cooling. KC1 -f 3CaO + 3CP = KC10 3 + 3CaCl 2 Calcium oxide. Calcium chloride. Potassium chlorate crystallizes in colorless, rhomboidal tables. When very thin they present an iridescent reflection. It melts at 400, and at a higher temperature is decomposed into oxygen and chloride and perchlorate of potassium, the latter of which is also decomposed when the temperature is raised still further. 2KC10 3 = KC1 -f KC10* -f O 2 KC10 4 = KC1 + O 4 Potassium chlorate deflagrates when thrown upon hot coals 5 when mixed with sulphur, it explodes by friction or percussion ; the detonation becomes dangerous if the sulphur be replaced by phosphorus. It is not very soluble in cold water. 100 parts of water at dissolve 3.3 parts, and at 24, 8.44 parts. It is much more soluble in boiling water. POTASSIUM PERCHLORATE. KC10* This salt is formed by the action of either heat or sulphuric acid upon potassium chlorate (page 124). It is but slightly soluble in water, requiring 65 parts at 15 for its solution. It crystallizes in anhydrous and transparent right rhombic prisms. Above 400 it decomposes into potassium chloride and oxygen. POTASSIUM CARBONATES. Potassium Neutral Carbonate, K 2 C0 3 . This carbonate is found in commerce under the simple name potash, and is known according to its source as Russian or American potash. N 25 290 ELEMENTS OF MODERN CHEMISTRY. It is obtained by lixiviating wood ashes ; that is, exhausting them with water, evaporating the solution to dryness, and cal- cining the residue in the air. The potash thus obtained is impure carbonate mixed with other salts of potassium, princi- pally the chloride and sulphate, and small quantities of silicate. It contains from 60 to 80 per cent, of carbonate. Potassium carbonate is now manufactured from the native chloride, Stassfurth salt, by a process similar to that which will be described for the manufacture of sodium carbonate from common salt. Pure potassium carbonate may be prepared by calcining potas- sium acid tartrate, or cream of tartar, at a red heat. A black mass is thus obtained from which water dissolves pure potas- sium carbonate, and the solution is evaporated to dryness. Neutral potassium carbonate is very soluble in water, and absorbs moisture from the air. 1 part of the anhydrous salt dissolves in 1.05 parts of water at 3, and in 0.49 parts at 70 (Osann). The solution has a decided alkaline reaction. A very concentrated hot solution deposits rhombic octahedra containing K 2 C0 3 -f- 2H 2 on cooling. Potassium Acid Carbonate, KHCO 3 . When a current of carbonic acid gas is passed into a concentrated solution of potas- sium neutral carbonate, the gas is absorbed, and crystals of potassium acid carbonate, ordinarily known as bicarbonate of potassa, are formed. It represents carbonic acid in which a single atom of hydro- gen is replaced by an atom of potassium. CO 2 + H 2 = HPCO* carbonic acid (hypothetical). CO 2 + KHO = JJ | CO 3 potassium acid carbonate. CO 2 + K 2 = K 2 C0 3 potassium carbonate. Potassium acid carbonate readily crystallizes in oblique rhom- bic prisms. It is much less soluble in water than the neutral carbonate, and its solution disengages carbonic acid gas on boiling. Its reaction is alkaline. Characters of Potassium Salts. The salts of potassium communicate a violet tint to flame. Their solutions are not precipitated either by hydrogen sulphide, ammonium sulphide, or sodium carbonate. Perchloric acid occasions a white precipitate of potassium perchlorate. SODIUM. 291 Platinum tetrachloride produces a yellow, crystalline precipi- tate of platinum and potassium double chloride, 2KCl.PtCl 4 . Hydrofluosilicic acid forms a white, gelatinous precipitate consisting of potassium fluosilicate. SODIUM. Na == 23 Sodium was discovered by Sir Humphry Davy in 1807. It is made by decomposing sodium carbonate with charcoal, a certain proportion of chalk being added to render the mixture infusible. The operation is conducted in large cast-iron cylin- FIG. 98. ders covered with a refractory luting to enable them to resist the high temperature required to effect the decomposition. The vapor passes into a flattened receiver in which the sodium condenses, and from which it runs into appropriate vessels (Fig. 98). 292 ELEMENTS OF MODERN CHEMISTRY. This metal is soft at the ordinary temperature. It has a silvery lustre, melts at 90.6, and distils at a red heat. It is not as avid of oxygen as potassium ; it can be melted in the air without taking fire. When thrown upon water, it melts and runs around on the surface, producing a hissing noise. The water is decomposed with disengagement of hydrogen and the formation of sodium hydrate. The reaction is analogous to that of potassium upon water, but is less energetic; fre- quently, however, it terminates by an explosion. If sodium be thrown upon hot water, or water which has been thickened with gum or starch, so that the consistence of the liquid may prevent the globule from moving rapidly, the latter becomes sufficiently heated to ignite the hydrogen evolved, which then burns with a yellow flame. The compounds of sodium are widely diffused in nature, and generally present great analogies with the corresponding potas- sium compounds. OXIDES AND HYDRATE OF SODIUM. Two oxides of sodium are known, a monoxide, Na 2 0, and a dioxide, Na 2 2 . Sodium, hydrate, NaOH, is frequently employed in the lab- oratory and in the arts under the name caustic soda. It is prepared by decomposing a rather dilute, boiling solution of so- dium carbonate by milk of lime, in the manner described for the preparation of potassium hydrate (page 283). It occurs as a white solid, which attracts moisture and carbonic acid from the air, and finally becomes transformed into a dry mass of carbonate. Sodium hydrate is freely soluble in water, and is very caustic. It is known in commerce as concentrated lye. SODIUM SULPHIDE AND SULPHYDRATE. Sodium sulphide, Na 2 S, is prepared by the following pro- cess: A concentrated solution of sodium hydrate is divided into two equal parts ; one part is then saturated with hydrogen sulphide, sodium sulphydrate being formed. NaOH + H 2 S = NaSH + H 2 Sodium hydrate. Sodium sulphydrate. SODIUM CHLORIDE. 293 To this sulphydrate the other portion of sodium hydrate is added, and the solution is concentrated out of contact with the air. Hydrated crystals of sodium sulphide are deposited. NaSH + NaOH = H 2 + Na 2 S These crystals are rectangular prisms terminated by four- faced points. When pure, they are colorless; they are very soluble in water. SODIUM CHLORIDE. NaCl This body is common salt, or sea-salt. It is widely diffused in nature. It is found in the solid state, as rock-salt, in large deposits in many countries. Sea-water contains a large proportion of sodium chloride, and this salt also exists in a number of mineral waters, of which it forms the most abundant constituent. In France, the greater portion of the salt delivered to com- merce is obtained by the evaporation of sea-water in the salt- marshes near the ocean, and the salt-basins along the Mediter- ranean. These are extensive basins into which the water is led from the sea, and where it forms a shallow layer, which is continually swept by the summer winds. It thus becomes con- centrated, and the concentration is favored by the water being continually kept in motion from one basin to another, until it arrives in the areas where the salt is deposited. The mother- liquors, from which the sodium chloride is separated, and which are still saturated with that salt, contain, in addition, magne- sium sulphate and salts of potassium. By cooling them to a low temperature sodium sulphate is obtained, being formed by a double decomposition between the sodium chloride and the magnesium sulphate. The new mother-liquor then deposits, first, potassium and magnesium double sulphate, and after- wards, magnesium and potassium double chloride (Balard). It was in the latter of these liquors that Balard discovered bro- mine in 1826. Sodium chloride is also obtained by the evaporation of the waters of salt springs. The operation is conducted in large sheet-iron boilers ; the salt crystallizes from the hot liquid, and a double sulphate of calcium and sodium, which is but slightly soluble, deposits in the basins in the course of time. 25* 294 ELEMENTS OF MODERN CHEMISTRY. Sodium chloride crystallizes from its aqueous solution in cubes. The crystals are generally small, and a great number of them frequently become agglomer- ated in symmetrical hopper-like masses (Fig. 99). These crystals are anhy- drous, but contain a small quantity of interposed water ; when heated they decrepitate, because this water is vola- FIG. 99. tilized and suddenly separates the crys- tals. Rock-salt is sometimes found in transparent cubes, sometimes in octahedra and intermediate forms. Sodium chloride fuses at a red heat and solidifies to a crystalline mass on cooling. It volatilizes at a white heat. It is very soluble in water, and its solubility does not increase with the temperature. According to Gay-Lussac, 1 part of common salt dissolves in 2.78 parts of water at 14 " " " 2.7 " " 60 " " " 2.48 " " 109.7 The saturated solution boils at 109.7 ; its density at 8 is 1;205. Sodium chloride is insoluble in absolute alcohol. SODIUM SULPHATE. This salt is obtained in the arts by decomposing common salt with sulphuric acid (page 117). This operation, which constitutes the first step in the manu- facture of sodium carbonate, is conducted in a reverberatory furnace, connected with a suitable apparatus for the condensa- tion of the hydrochloric acid which is disengaged. Sodium acid sulphate is first formed, and at a higher temperature this reacts upon another molecule of sodium chloride. + NaCl = Na 2 SO + HC1 Sodium acid sulphate. Sodium sulphate. Sodium sulphate is now extensively produced by subjecting the mother-liquors from the manufacture of salt from sea-water to intense cold. It crystallizes from water in four-sided, oblique rhombic prisms, containing 10 molecules of water of crystallization; SODIUM CARBONATE. 295 these crystals effloresce in the air. They possess a bitter, salty, and disagreeable taste. They are very soluble in water, and the temperature of their maximum solubility is 33. Accord- ing to Gay-Lussac, 100 parts of water at dissolve 12 parts of sodium sulphate. u is " 48 " " 25 " 100 " " < 33 " 332.6 " " 5QQ 263 " " When the solution saturated at 33 is heated, it deposits an- hydrous sodium sulphate in orthorhombic octahedra, analogous to the anhydrous sodium sulphate found in nature (thenardite). Sodium Acid Sulphate, ^ I SO 4 . This salt may be ob- tained by dissolving in water the requisite proportions of so- dium neutral sulphate and sulphuric acid. On cooling the saturated solution, oblique rhombic prisms are obtained, which, according to Mitscherlich, contain two molecules of water of crystallization. These crystals are very soluble in water, and have an acid taste. Alcohol decomposes them into sulphuric acid, which dissolves, and neutral sulphate, which precipitates. SODIUM CARBONATE. Na 2 CO 3 This important salt, known also as soda and sal-soda, is manufactured on an immense scale in the arts. It is used in the manufacture of soap and glass, for washing, and many other purposes. It was formerly obtained from the ashes of fuci, algae, and other sea-plants which furnished Alicant soda. It is now most generally prepared from sodium chloride, and the process, which is due to Le Blanc, consists of three distinct operations: 1st, the transformation of the sodium chloride into sulphate by sulphuric acid ; 2d, the conversion of the sul- phate into carbonate by calcination with a mixture of chalk and coal ; 3d, lixiviation of the calcined mass and evaporation of the solution. Only the latter two operations need be de- scribed here : they are conducted in reverberatory furnaces, of which the doubly-arched roofs are licked by the flame of the combustible (Fig. 100). 296 ELEMENTS OF MODERN CHEMISTRY. A mixture of 1000 parts of sodium sulphate, 1040 parts of chalk, and 580 parts of coal, is first introduced into compart- ment B of the furnace, where it is dried. It is then transferred to compartment A, where the temperature is very elevated, and where the sodium sulphate is reduced to sulphide by the FIG. 100. coal. The sodium sulphide and chalk react upon each other, forming sodium carbonate and calcium sulphide (Kolb). The results of the reaction may be expressed by the follow- ing equation : Na 2 S0 4 + CaCO 3 + O = Na 2 C0 3 -f CaS + 4CO. There are, however, certain secondary reactions which take place at the same time ; thus, a certain quantity of sodium oxide is formed by the action of the coal upon the carbonate. Na 2 C0 3 + C = 2CO + Na 2 When the incandescent mass has become pasty, it is removed from the furnace, reduced to powder, and thoroughly lixiviated. The water dissolves the sodium carbonate, and leaves the in- soluble calcium sulphide, which remains mixed with the lime produced by the decomposition of the excess of chalk employed (Gossage, Scheurer-Kestner). The solutions are concentrated in the boiler D, heated by the waste heat from the soda fur- nace. Finally, they are drawn off into the compartment C, where they are evaporated to dryness. The sal-soda of com- merce is thus obtained. When the properly-concentrated solu- tion is allowed to cool, the crystallized soda of commerce is deposited. Another process, proposed by Schloesing and Holland, is also used for the fabrication of sodium carbonate. SODIUM CARBONATE. 29*7 It depends upon the double decomposition which takes place between ammonium acid carbonate and sodium chloride in concentrated aqueous solution. NaCl -f (NH 4 )HC0 3 = NIPC1 + NaHCO 3 The sodium acid carbonate, which is but slightly soluble, is precipitated ; it is collected and converted into the neutral car- bonate by the action of heat. 2NaHC0 3 = Na 2 C0 3 + CO 2 + H 2 It thus loses half of its carbonic acid, which is utilized for the preparation of a new quantity of ammonium acid carbonate. The other portion of the carbonic acid necessary for this oper- ation is produced by the calcination of lime-stone (calcium car- bonate), which at the same time yields the lime necessary for the liberation of the ammonia contained in the mother-liquor in the form of ammonium chloride. A considerable quantity of sodium chloride is also manufac- tured from cryolite, which is a double fluoride of sodium and aluminium, and of which large deposits exist in Greenland. The mineral is calcined with lime, calcium fluoride and alunii- nate of soda being formed. APFl 6 ,6NaFl + 6CaO = GCaFl 2 + Al 2 3 ,3Na 2 Cryolite. Calcium fluoride. Aluminate of soda. The latter compound is dissolved out by water and decom- posed by carbonic acid gas, aluminium oxide being precipitated and sodium carbonate remaining in solution. Sodium carbonate crystallizes in oblique rhombic prisms, containing 10 molecules of water of crystallization. When heated, they fuse in this water of crystallization, which they then abandon ; they also lose it by efflorescence when exposed to the air. Sodium carbonate is very soluble in water, and the solution has a strongly alkaline reaction. According to Poggiale, 100 parts of water at dissolve 7.08 parts of sodium carbonate. 10 " 16.06 " " 20 " 25.93 25 " 30.83 " " 30 " 35.90 " " 104.6 " 48.5 " " The saturated solution boils at 104.6. Sodium carbonate is insoluble in alcohol. N* 298 ELEMENTS OF MODERN CHEMISTRY. Sodium Acid Carbonate, NaHCO 3 . When carbonic acid gas is passed into a solution of sodium carbonate or over crystals of that salt, the gas is absorbed and sodium acid car- bonate, commonly called bicarbonate of soda, is formed. This salt crystallizes in oblique, four-sided prisms, shortened into the form of tables. Its taste is salty and slightly alkaline. It is less soluble in water than the neutral carbonate. It restores the blue color to reddened litmus ; its solution does not pre- cipitate that of magnesium sulphate. When boiled, it loses carbonic acid, neutral carbonate being formed. PHOSPHATES OF SODIUM. There are three phosphates of sodium derived from ordinary or otho-phosphoric acid. H) Na) Na) Na) PO 4 H V PO 4 + 2H 2 Na } PO* + 12H 2 Na [ PO* + 12H 2 H I Hj HJ Hj Hj NaJ Phosphoric Monosodium Disodium phosphate. Trisodium phosphate, acid. phosphate. Monosodium phosphate is acid, the disodium is neutral, and the trisodium has an alkaline reaction. Disodium phosphate, or, as it is frequently called, common or neutral phosphate of soda, is the most important. It is prepared by neutralizing the cal- cium acid phosphate, obtained by digesting bone-dust with dilute sulphuric acid and filtering, with sodium carbonate. Tricalcium phosphate is precipitated, and disodium phosphate remains in solution. By evaporation of the filtered liquid, the salt may be obtained in voluminous, transparent, oblique rhombic prisms, containing 12 molecules of water of crystallization. SODIUM BORATE, OR BORAX. This salt corresponds to a boric acid containing 2Bo 2 3 -f- H'O = H 2 Bo*0 7 . It results from the action of one molecule of sodium oxide upon two molecules of boric oxide. 2(Bo 2 3 ) -j- Na 2 = Na 2 Bo 4 7 It crystallizes with either 10 or 5 molecules of water. Borax was formerly obtained from Asia, where it exists in solution in the waters of certain lakes. By the evaporation LITHIUM. 299 of these waters a product known as tinkal was obtained ; this is natural borax; it crystallizes in oblique rhombic prisms. Borax is found in abundance in certain lakes in California. A great part of the borax of commerce is obtained by satu- rating the boric acid of Tuscany with sodium carbonate, and causing the solution to crystallize below 56. If the boiling solution be very concentrated, it deposits between 79 and 56 crystals which are octahedral and contain only 5 molecules of water of crystallization. The two varieties of borax, the prismatic and the octahedral, differ then in their proportions of water of crystallization. When borax is heated, it melts in its own water, swells up and becomes dry, and then undergoes igneous fusion. Melted borax dissolves a great number of oxides and forms with them variously-colored glasses on cooling. It dissolves in 12 parts of cold and 2 parts of boiling water ; the solution has a faint alkaline reaction. Characters of Sodium Salts. Sodium salts are not pre- cipitated from their solutions by either hydrogen sulphide, ammonium sulphide, sodium carbonate, or platinic chloride. Hydrofluosilicic acid forms with them a white precipitate. A solution of potassium antimonate produces a white precipitate of sodium antimonate (Fremy). Sodium salts impart a yellow color to flames. A small quantity of alcohol may be ignited in a saucer and will burn with an almost colorless flame, but the introduction of a small quantity of sodium hydrate, chloride, or any other sodium compound, at once colors the flame bright yellow. This character is very sensitive, and the smallest trace of sodium may thus be recognized by introducing a platinum wire, dipped into the substance to be tested, into the colorless flame of the blow-pipe or of a Bunsen burner. LITHIUM. Li = 7 In 181*7, Arfvedson, a Swedish chemist, discovered a new alkali, lithia, which is the hydrate of lithium, LiOH, analogous to potassium hydrate, KOH. To this hydrate corresponds an oxide, Li' 2 O, and a chloride, LiCl. Bunsen was the first to ob- tain the metal lithium, which he prepared by electrolysis of the 300 ELEMENTS OF MODERN CHEMISTRY. fused chloride. It is a silvery-white metal, but its surface rap- idly tarnishes in the air. It is the lightest of the solid ele- ments, its density being between 0.578 and 0.589. It melts at 180. It is less oxidizable than either sodium or potassium. When heated above its point of fusion in the air or in oxygen, it burns with a brilliant white flame. It decomposes water at ordinary temperatures, but without melting like sodium. The salts of lithium are soluble in water, but the carbonate and phosphate only slightly so. There exists also a double phosphate of sodium and lithium, which is but slightly soluble. The salts of lithium communicate a red color to the flame of alcohol or of the Bunsen burner. The compounds of lithium are generally prepared from the native silicate known as lepidolite. (LE8IUM AND RUBIDIUM. SPECTRUM ANALYSIS. Caesium and rubidium are two alkaline metals discovered by Kirchhoff and Bunsen in 1860-61, by the aid of a new method of analysis. This method consists in the examination of spectra ; hence the name spectrum analysis. The solar spectrum formed upon a screen which intercepts a beam of solar light refracted by passage through a prism, con- sists of a series of colored bands. The different simple rays of which white light is composed are unequally refracted by the prism, and separate from each other on their emergence. The violet rays, which are farthest turned from their primitive direction, form the most deviated extremity of the spectrum. The red rays, which are the least refracted, form the least de- viated extremity. The visible spectrum of solar light presents not only a succession of variously-colored bands ; when it is closely examined by the aid of magnifying instruments, it is found that the succession is not continuous, but that the lumi- nous bands are traversed by dark lines. These lines, which were discovered by Wollaston and studied by Fraunhofer, are very numerous, and are irregularly distributed throughout the spectrum, from the red to the violet, but each one of them occupies a definite position, and for the principal lines that position has been determined by exact measurements. Fraun- CESIUM AND RUBIDIUM. 301 hofer designated them by the letters A, B, C, D, E, F, Gr, H. The D line is the most distinct of all : its place is in the yel- low. Other lights, the stars, for example, give similar discon- tinuous spectra. On the contrary, an incandescent platinum wire, or any other luminous source which contains no volatile matter, gives a continuous spectrum. Very interesting facts are observed when the sources of light are flames into which the vapors of volatile substances, par- ticularly the metallic salts, are introduced. The spectra of such flames are formed exclusively of brilliant lines (see plate). If a platinum wire which has been dipped into a solution of sodium chloride be introduced into the colorless flame of a Bunsen burner, the flame will assume a yellow color, and will give a visible spectrum, but one which is very incomplete, since it consists of a single yellow line. It has been found that this line exactly coincides with the dark line D, existing in the yellow of the solar spectrum. This line characterizes sodium in all of its compounds : it is the spectrum of sodium. In the same manner, a flame into which a compound of potas- sium, lithium, barium, calcium, or other volatile metal is intro- duced, will give for each metal a particular spectrum formed of variously-colored lines. Each is perfectly characterized by the number, color, and position of the lines. Barium gives the most numerous and the widest lines ; other metals give more compli- cated spectra. That of iron is composed of 70 brilliant lines. Kirchhoff and Bunsen, who discovered these facts, made a happy application of them to analysis. To detect the presence of a metal in a compound or even in a mixture, a small portion of the substance is introduced into a colorless gas flame, and the spectrum then given by the flame is observed by the aid of an instrument called a spectroscope. The method is so sensitive that -g-.oiru'.'UTrs' f a milligramme of sodium chloride will render the yellow sodium line distinctly visible. The discovery of two new metals, caesium and rubi- dium, crowned the brilliant researches of Kirchhoff and Bunsen. Since then, three other new metals have been discovered by the aid of spectrum analysis : thallium, which gives a green line, indium, which gives an indigo-blue line, and gallium, which gives two violet lines very close together. Thallium was discovered by Crookes and Lamy, indium by Reich and Richter, and gallium, the discovery of which was most remarkable of all, by Lecoq de Boisbaudran. 26 302 ELEMENTS OF MODERN CHEMISTRY. THALLIUM. The beautiful green line given by this metal was first ob- served by William Crookes, who regarded it as characteristic of a new element. The honor of having isolated the latter and establishing its true character belongs to Lamy. Thallium is a heavy metal which resembles lead in certain of its properties. It melts at 200; its density is 11.9. It forms an oxide, TPO; a crystallizable hydrate, T10H, which is soluble in water and also caustic ; a monochloride, T1C1, and a moniodide, Til. These compounds relate it to the alkaline metals, but others, which include an oxide, TPO 3 , and a trichlo- ride, T1CP, separate it from that class. Its principal com- pounds have been studied by Lainy and Willm. BAEIUM Bunsen obtained barium by the electrolysis of fused barium chloride ; this metal is very avid of oxygen, and tarnishes rapidly. It decomposes cold water. Barium Oxide, or Baryta, BaO. Barium oxide is obtained by calcining barium nitrate. Its nature was first recognized in 1808, by Davy, who decomposed it by the voltaic current. It is a gray, porous substance, which unites energetically with water, producing a hissing noise and a great disengagement of steam, due to the elevation of temperature. The product of the reaction is a white hydrate, ordinarily known as caustic baryta. BaO + H 2 = Ba(OH) 2 Barium oxide. Barium hydrate. Barium hydrate is soluble in two parts of boiling water, and on cooling is in great part deposited in large tabular crystals, containing 8 molecules of water. The solution of barium hy- drate in water is called baryta water. Barium Dioxide, BaO 2 . When dry oxygen is passed over barium oxide heated to dull redness, the gas is absorbed and a dioxide, BaO 2 , is formed. It is a gray, porous mass, some- times greenish. It loses one atom of oxygen at a bright-red heat. When brought in contact with water, it combines with BARIUM SALTS. 303 the latter quietly and without disengagement of heat, forming a pulverulent hydrate. When treated with sulphuric acid, barium dioxide disen- gages oxygen mixed with ozone. When its hydrate is intro- duced into hydrochloric acid, hydrogen dioxide is formed. Barium Sulphide, BaS. This is obtained by reducing barium sulphate with charcoal. BaSO* + C 4 = BaS + 4CO Barium sulphate. Barium sulphide. The sulphate is reduced to fine powder, and is mixed with a certain quantity of flour or rosin. The mixture is then made into a paste with linseed oil, and shaped into little balls. These are calcined at a bright-red heat in a covered crucible, and a porous, gray mass is thus obtained which, when treated with boiling water, yields a solution which deposits hexagonal tables after filtration and cooling. These crystals do not present a very constant composition : it is a mixture of sulphide, sulphy- drate, and hydrate of barium. Their solution has a light-yel- low color. BARIUM SALTS. Barium Chloride, BaCl 2 -J- 2H 2 0. This salt is obtained by saturating the solution of barium sulphide with hydrochloric acid. Hydrogen sulphide is disengaged ; the solution is boiled, filtered, and evaporated to crystallization. Barium chloride separates in quadrangular tables belonging to the type of the right rhombic prism. These crystals are inalterable in the air. 100 parts of water at 18 dissolve 43.5 parts of barium chlo- ride, and 78 parts at 105.5, the temperature of ebullition of the saturated solution (Gay-Lussac). Absolute alcohol dis- solves ^Lg- of its weight of barium chloride. Barium Nitrate, Ba(N0 3 ) 2 . Barium nitrate is prepared by decomposing barium sulphide or carbonate with dilute nitric acid, and filtering and evaporating the solution. It crystallizes in regular octahedra, or in cubo-octahedra. The crystals are transparent and unaltered in the air. One part of this salt requires for its solution 20 parts of water at 0.12; 5 parts of water at 15; 2.8 parts at 106, the tem- perature of ebullition (Gay-Lussac). When heated to redness, barium nitrate gives off oxygen, nitrogen, and red vapors, leaving a residue of oxide, BaO. 304 ELEMENTS OP MODERN CHEMISTRY. Barium Sulphate, BaSO. This salt is found abundantly in nature as heavy spar, and sometimes occurs in right rhom- bic crystals. It is entirely insoluble in water and acids, with the exception of concentrated sulphuric acid. It is precipi- tated as a finely-divided, amorphous powder when sulphuric acid or a soluble sulphate is added to a solution, even very di- lute, of a salt of barium. Barium Carbonate, BaCO 3 . Barium carbonate constitutes an amorphous, white powder, which is obtained by double de- composition on adding solution of sodium carbonate to a solu- tion of barium sulphide. Natural barium carbonate is an abundant mineral, and is found crystallized in right rhombic prisms ; it is called witherite. Characters of Barium Salts. Barium salts are precipi- tated neither by hydrogen sulphide nor by ammonium sulphide. Sodium carbonate produces in them a white precipitate. Even when very dilute, the barium salts produce a white precipitate with sulphuric acid, which is insoluble in either cold or boiling nitric acid. STRONTIUM. Sr = 87.5 The compounds of this metal present great analogies to those of barium. Strontium was discovered by Davy in 1808, but the metal was isolated by Bunsen and Matthiessen by the aid of a process similar to that which serves for the preparation of barium. Matthiessen describes it as a yellow metal, having a density of 2.50-2.58, harder than lead, and decomposing cold water. Strontium forms two oxides, a monoxide, SrO, and a dioxide, SrO 2 . Strontium chloride, SrCl 2 , crystallizes in deliquescent needles which contain three molecules of wafer of crystallization. It is very soluble in water and slightly soluble in alcohol ; the alcoholic solution burns with a red flame. Strontium nitrate, Sr(N0 3 ) 2 , which is prepared like barium nitrate, is deposited from its hot aqueous solution in anhydrous octahedra, and crystallizes at low temperatures in oblique rhom- bic tables containing 5 molecules of water of crystallization (Laurent). The carbonate of strontium, SrCO 3 (strontianite), and the CALCIUM. 305 sulphate, SrSO 4 (celestine), are found native. These two salts are insoluble in water, and are deposited as white precipitates on adding a soluble carbonate or sulphate to the solution of a strontium salt. Strontium sulphate is less insoluble, however, than barium sulphate. CALCIUM. Ca = 40 Lime, which is universally known, is the oxide of a metal called calcium. According to Lies-Bodard and Jobin, calcium may be obtained by decomposing calcium iodide with sodium in an iron crucible. Matthiessen obtained it by decomposing fused calcium chloride by the voltaic current. Calcium has a yellow color when freshly filed, but it tarnishes rapidly in moist air and becomes covered with a grayish layer of hydrate. When heated upon platinum-foil, it takes fire and burns with a dazzling flame. It decomposes water at ordinary temperatures. OXIDE AND HYDRATE OF CALCIUM. Lime, or calcium oxide, CaO. is obtained by calcining the carbonate in peculiar furnaces, which are called lime-kilns. It occurs as large, compact, and hard grayish masses, which con- stitute quick-lime. It is infusible, even at the highest temperatures. When exposed to the air, it attracts moisture and carbonic acid, aug- ments in volume, and is finally converted into a white powder, a mixture of calcium hydrate and carbonate. When lime is sprinkled with water, it absorbs the liquid without giving rise to any particular phenomenon ; but in a little while, the pieces saturated with water become hot, give off steam, and then they split and increase in volume. If enough water be used, the quick-lime will be converted into a white powder, which is called slaked lime; it is calcium hydrate. CaO + H 2 = Ca0 2 H 2 = Ca(OH) 2 When slaked lime is suspended in water, a white, creamy liquid is obtained that is called milk of lime. If this be fil- tered or allowed to settle, the clear, limpid liquid resulting will have an alkaline reaction, for it contains a small quantity of 26* 306 ELEMENTS OP MODERN CHEMISTRY. calcium hydrate in solution : it is lime-water. Calcium hydrate is more soluble in cold than in hot water. Employment of Lime in Constructions. Lime is largely employed for building purposes in both ordinary and submarine constructions. The limestone which is used for the preparation of lime is rarely pure, and consequently the product of its cal- cination presents different qualities, according to the propor- tions of foreign matters which remain in the lime, and which consist of a small quantity of magnesia, oxide of iron, and especially clay. Fat limes are those produced by the calcina- tion of almost pure limestones; they develop much heat, and swell up very much on slaking. Such lime forms an unctuous and binding paste with water, and forms ordinary mortar when mixed with sand. Impure linrestones yield lean lime, contain- ing magnesia, oxide of iron, and clay. It is gray, and develops but little heat and increases but slightly in volume on slaking. The calcination of limestone containing from 10 to 30 per cent, of clay produces hydraulic lime. Such lime sets under water, that is, the mortar solidifies after a few days, and becomes very hard, even when immersed in water. On account of this curious property it is used in submarine constructions. Such lime is yellow ; slaking it produces but little heat, and scarcely any in- crease in volume. The hydraulic mortar formed by its mix- ture with sand will harden under water. Mortars possessing this property may also be prepared by mixing lime with baked argillaceous materials, such as powdered tiles, pottery, bricks, etc. Certain argillaceous rocks of volcanic origin, the pozzolana so abundant near Vesuvius, for example, yield an excellent hydraulic lime when mixed with fat lime. Cement is a variety of lime resulting from the calcination of limestones containing from 40 to 50 per cent, of slate. When mixed with water, such cement sets in a few minutes in a solid mass like plaster. Vicat has shown that the different varieties of hydraulic lime and cement can be prepared by properly calcining carbonate of lime, or chalk, with various proportions of clay. According to him, ordinary mortar sets because the lime gradually absorbs carbonic acid gas from the air, forming a carbonate which hardens and binds together the grains of sand. The hardening of hydraulic lime and mortar is due to another cause : the clay which they contain in the anhydrous state tends to become hydrated and to form a double silicate of calcium and aluminium, or a silicate and aluminate of calcium, CALCIUM CHLORIDE CALCIUM NITRATE. 307 insoluble compounds, which become very coherent on contact with water. CALCIUM CHLORIDE. CaCl 2 This salt is prepared by dissolving white marble or chalk in hydrochloric acid. When the solution is concentrated it deposits large, six-sided prisms, containing 6 molecules of water of crys- tallization. They are very deliquescent and produce a depres- sion of temperature when they are dissolved in water. If they be mixed with their own weight of snow or powdered ice, a cold of 45 may be produced. When they are heated, they melt in their water of crystalliza- tion, of which they lose 4 molecules at 200, and the remainder at a red heat ; at the latter point the mass enters into igneous fusion. On cooling, the fused calcium chloride solidifies to a white, crystalline mass, in which form it is ordinarily employed for the desiccation of gases. Calcium chloride dissolves readily in alcohol. CALCIUM NITRATE. Ca(NO 3 ) 2 -f 4H 2 O This salt is formed naturally in the neighborhood of dwell- ings, in the soils of cellars, and in damp walls. It is contained in what are known as saltpetre materials ; it exists in certain spring and well waters. It may be made by saturating nitric acid with calcium carbonate. It is very soluble in water and in alcohol. It crystallizes with difficulty in six-sided, oblique rhombic prisms, which contain 4 molecules of water of crys- tallization : they are deliquescent. CALCIUM CARBONATE. (CARBONATE OF LIME.) CaCO 3 Calcium carbonate is found in great abundance in nature, and under different forms. It exists crystallized as Iceland spar and aragonite ; the former crystallizes in colorless, trans- parent, and doubly refracting rhombohedra ; the latter in right rectangular prisms. 308 ELEMENTS OF MODERN CHEMISTRY. Marble, the various limestones, and chalk, constitute other varieties of natural calcium carbonate. Pure water dissolves but feeble traces of this salt; water charged with carbonic acid dissolves a larger quantity, converting it into dicarbonate. It is in this state that it is contained in hard waters. Calcium carbonate may be prepared by double decomposition between solutions of sodium carbonate and calcium chloride. When heated to bright redness, it is completely decomposed into lime and carbonic anhydride. CALCIUM SULPHATE. CaSO* This salt exists in two states in nature : anhydrous, it con- stitutes the anhydrite of mineralogists ; combined with two molecules of water of crystallization, it forms gypsum or plas- ter stone. Gypsum sometimes occurs in lance-head-shaped crystals, grouped together ; they are divisible into thin, trans- parent layers, easily scratched by the finger-nail. Certain varieties of gypsum constitute alabaster. All the forms of hydrated calcium sulphate contain 21 per cent, of water. When heated to 80 in the air, or to 115 in closed vessels, the sulphate, CaSO 4 -f 2H 2 0, abandons its water of crystalli- zation and is converted into the anhydrous sulphate. Between 120 and 130, this dehydration is rapid and complete. It is operated on the large scale in plaster furnaces. In this state calcium sulphate will readily recombine with its water of crystallization. If the plaster be calcined at too high a tem- perature it will not again become hydrated. If powdered plaster of Paris be mixed with enough water to form a creamy liquid, it may be poured into a mould, and in a few minutes will harden to a compact mass, completely filling every cavity of the mould. In becoming hydrated, the particles of calcium sulphate assume the crystalline form and increase in volume. These properties render plaster of Paris valuable in building operations. It is also employed to a large extent in agriculture. Calcium sulphate is but slightly soluble in water. 1000 parts of boiling water dissolve a little more than 2 parts of the salt; at 35 they dissolve 2.64 parts; at 20, 2.05 parts. CALCIUM HYPOCHLORITE. 309 CALCIUM HYPOCHLORITE. Ca(ClO) 2 Calcium hypochlorite exists in a product largely employed in the arts under the name of chloride of lime, and which is obtained by exposing well-hydrated lime to the action of chlo- rine ; it is a mixture of calcium chloride and calcium hypo- chlorite. 4C1 2CaO = CaCP + Ca(ClO) 2 Calcium chloride. Calcium hypochlorite. The operation is conducted by passing a current of chlorine over slaked lime placed in thin layers upon shelves arranged in the walls of masonry chambers. The chlorine is made in earthenware vessels, A (Fig. 101), heated in a water-bath; it FIG. 101. is washed in the jars D, and then conducted into the upper part of the chamber by the tube G. In order to insure the preservation of the chloride of lime, an excess of lime is always left in it. 310 ELEMENTS OF MODERN CHEMISTRY. Chloride of lime is a powerful bleaching agent ; it owes this property to the calcium hypochlorite which it contains, and which is decomposed by the action of acids. If hydrochloric acid be added to a solution of chloride of lime, chlorine gas is at once disengaged with effervescence. The reaction may be conceived to take place in two phases. The hydrochloric acid acts upon the hypochlorite, forming hypochlorous acid. 2HC1 + Ca(ClO) 2 = CaCP + 2HC10 Calcium hypochlorite. Calcium chloride. Hypochlorous acid. The hypochlorous acid thus set free then reacts with the calcium chloride, forming calcium hydrate and chlorine. CaCP + 2HC10 = Ca(OH) 2 -f 2C1 2 The calcium hydrate is in the presence of an excess of hy- drochloric acid, by which it is reconverted into calcium chlo- ride. The latter salt is thus continually decomposed and re-formed. Chloride of lime is also decomposed by less energetic acids, even by carbonic acid gas. When a solution of chloride of lime is boiled, the hypochlo- rite which it contains is converted into chlorate and chloride. 3Ca(C10) 2 = Ca(C10 3 ) 2 + 2CaCP Calcium hypochlorite. Calcium chlorate. Characters of Calcium Salts. Calcium salts are not pre- cipitated either by hydrogen sulphide or ammonium sulphide. Sodium carbonate forms in them a white gelatinous precipitate. Sulphuric acid and the soluble sulphates produce a white pre- cipitate, if the calcium solutions be concentrated or only mod- erately dilute. Oxalic acid, or better, ammonium oxalate, produces a white precipitate of calcium oxalate, even in the most dilute solutions of calcium salts. MAGNESIUM. Magnesium was discovered by Bussy. Matthiessen obtained it by decomposing fused magnesium chloride by electricity. Preparation. Deville and Caron recommend the following- process for the preparation of considerable quantities of mag- MAGNESIUM OXIDE MAGNESIUM CHLORIDE. 311 nesium. A mixture of 600 grammes of anhydrous magnesium chloride, 100 grammes of sodium chloride, 100 grammes of calcium fluoride, and 100 grammes of sodium cut into small pieces is heated to redness in a covered crucible. The magne- sium chloride is reduced by the sodium, and the magnesium set free collects in little globules disseminated in the fused mass, which must be stirred with an iron rod. These little globules are removed from the scoriae when cold, introduced into a charcoal boat, and heated to bright redness in a current of hydrogen. The magnesium volatilizes and condenses far- ther on in the tube ; it may then be fused with a flux consisting of magnesium chloride, sodium chloride, and calcium fluoride. The metal collects at the bottom of the crucible. Properties, Magnesium has a density of 1.74 or 1.75. It fuses at 500. It decomposes water at ordinary temperatures but slowly. It may readily be rolled into ribbon or drawn into wire. The wire is grayish and not very brilliant. The end of a bundle of these wires may be heated in an alcohol lamp until they take fire, and the whole may then be plunged into a jar of oxygen. They burn with an incomparable splendor that the eye cannot support; at the same time the jar becomes filled with a white smoke, which condenses into a white powder, the product of the combustion ; it is magnesia, the oxide of mag- nesium. MAGNESIUM OXIDE, OR MAGNESIA. MgO This body is obtained by calcining white magnesia, or mag- nesium hydrocarbonate. It is a white, infusible, light, and insipid powder. It does not dissolve in water, but combines with that liquid forming a hydrate, Mg(OH) 2 = MgO.H'O. This hydrate slowly restores the blue color to reddened litmus- paper. Magnesium hydrate is precipitated when a solution of caustic potassa is added to the solution of a magnesium salt. Calcined magnesia is frequently employed in medicine. MAGNESIUM CHLORIDE. MgCP This salt is known in the anhydrous state and crystallized. Anhydrous magnesium chloride is prepared by dissolving the 312 ELEMENTS OF MODERN CHEMISTRY. carbonate in hydrochloric acid, adding ammonium chloride to the solution and evaporating to dryness. A double chloride of magnesium and ammonium is thus obtained which may be per- fectly dried ; the dry mass is introduced into a clay crucible and heated; the ammonium chloride volatilizes, while the magne- sium chloride remains, and solidifies on cooling to a colorless, pearly mass. It is very soluble in water, and when properly concentrated, the solution deposits deliquescent, prismatic crystals containing six molecules of water of crystallization. These crystals can- not be dehydrated, nor can their solution be evaporated to dryness, without decomposing the chloride by the action of the water; under these circumstances the magnesium chloride is converted into hydrochloric acid and magnesia. MgCP + H 2 = 2HC1 + MgO MAGNESIUM CARBONATE. MgCO 3 The anhydrous carbonate MgCO 3 (giobertite, magnesite) is found native, crystallized in rhombohedra, similar to those of calcium carbonate. Considerable deposits are also found of a double carbonate of magnesium and calcium, known as dolomite. When a boiling solution of magnesium sulphate is precipi- tated by an excess of sodium carbonate, carbonic acid gas is disengaged, and a precipitate is formed containing at the same time magnesium carbonate and magnesium hydrate (magnesium hydrocarbonate) . When this is dried, it constitutes the white magnesia of the pharmacies. MAGNESIUM SULPHATE. MgSO* + 7H 2 This salt exists in solution in sea- water and in certain purga- tive mineral waters, such as those of Sedlitz, in Bohemia, and Epsom, in England. Hence the names Sedlitz salt and Epsom salt, formerly given to this body. At Stassfurth, it is found crystallized with one molecule of water (kieserite) and mixed with the anhydrous sulphate. It is deposited from the mother-liquors of salt-marshes when they are evaporated at the natural summer heat (Balard). When it separates at ordinary temperatures from an aqueous ALUMINIUM. 313 solution that has been tolerably concentrated by heat, it crystal- lizes in transparent and colorless right rhombic prisms. At 0, it crystallizes with 12 molecules of water ; at 30, with 6 molecules; Its taste is disagreeable, at the same time salty and bitter. When magnesium sulphate crystallized with 7 molecules of water is heated, it first melts in its water of crystallization, of which it loses 6 molecules. At 132, it still retains one mole- cule, which it loses only at 210. It is very soluble in water; 100 parts of water at dis- solve 25.76 parts of the anhydrous sulphate, and 0.47816 part for every additional degree (Gray-Lussac). Magnesium sulphate forms a double sulphate with potassium sulphate, K 2 S0 4 .MgS0 4 + 6H 2 O. Characters of Magnesium Salts. They are precipitated by neither hydrogen sulphide nor ammonium sulphide. Sodium carbonate produces a white, flocculent precipitate. Potassium hydrate and ammonia form white precipitates, but ammonia will not precipitate magnesia from an acid solution or from one containing ammonium chloride. Sodium phosphate and ammonia together produce a granular precipitate of ammonio-magnesium phosphate. ALUMINIUM. Al -= 27 5 This metal long remained a chemical curiosity, and has only become common within a few years. It was discovered in 1827 by Wohler, and in 1854, H. Saint-Claire Deville succeeded in producing it on the large scale. It is obtained by decom- posing aluminium and sodium double chloride by sodium. AFCl 6 ,2NaCl + 3Na 2 = 8NaCl + AP In the arts, a mixture of sodium, aluminium and sodium double chloride, and cryolite, is projected into a reverberatory furnace heated to bright redness. The cryolite acts as a flux : it is a double fluoride of sodium and aluminium, found native in Greenland. Aluminium is a white metal, and has a somewhat bluish lustre when polished. It is ductile, malleable, very sonorous, and a good conductor of heat and electricity. It is as light as glass and porcelain, its density being only 2.56. o 27 314 ELEMENTS OF MODERN CHEMISTRY. Aluminium is unaltered by the air, even by moist air. When heated in thin sheets in a current of oxygen, it burns and is converted into alumina. Nitric and sulphuric acids scarcely attack it. Hydrochloric acid dissolves it rapidly, disengaging hydrogen. It is immediately attacked by boiling solutions of potassium or sodium hydrates; hydrogen is disengaged and alkaline aluminates are formed. ALUMINIUM OXIDE, OR ALUMINA. A1 2 O 3 Corundum, a very hard precious stone, consists of anhydrous alumina. It is named oriental ruby when it has a red color ; sapphire when it is blue, and oriental topaz when it has a yellow tint. Emery is a sort of opaque corundum ; it is gran- ular and colored by a small quantity of oxide of iron. When ammonium carbonate is added to a solution of alum, carbon dioxide is evolved, and a gelatinous precipitate of hy- drated alumina is formed. The precipitate dissolves readily in caustic potassa. When heated, it loses water and is converted into anhydrous alumina ; the latter is undecomposable by heat ; it fuses only in the flame of the oxy hydrogen blow-pipe. Gaudin has succeeded in pro- ducing fine precious stones that cannot be cut by the file, and at least as hard as rock-crystal, by melting Limoge emerald (anhydrous alumina) with various substances, such as sand, kaolin, talc, and lime, which are added as fluxes. Alumina cannot be reduced by charcoal at the highest tem- peratures ; it can only be reduced by the joint action of char- coal and chlorine ; aluminium chloride is then formed. ALUMINIUM CHLORIDE. A1 2 C1 When a current of chlorine is passed over an incandescent mixture of alumina and charcoal, aluminium chloride and carbon monoxide are formed (Oersted). APO 3 + 3C + Cl 6 = SCO -f APC1 6 Aluminium chloride thus formed is a white, crystalline sub- stance, sometimes having a light-yellow color. It is fusible, and ALUMINIUM SULPHATE ALUM. 315 volatilizes in the air at a temperature little above 100. When exposed to the air it gives off white fumes and attracts moist- ure. It dissolves in water with production of heat. A solution of aluminium chloride may be obtained by dis- solving gelatinous alumina in hydrochloric acid. When this solution is evaporated, it decomposes as soon as it attains a certain degree of concentration, disengaging hydrochloric acid, and leaving alumina. Aluminium chloride readily combines with sodium chloride, forming a double chloride, APCl 6 .2NaCl, fusible towards 200. ALUMINIUM SULPHATE. A1 2 (SO) 3 -f 18H 2 O This is obtained in the arts by decomposing non-ferruginous clays with sulphuric acid. It crystallizes with difficulty in needles and in thin, pearly scales. In this state it contains 18 molecules of water of crystallization. It dissolves in 2 parts of cold water. When heated, it first loses its water, and at a higher temperature it gives off sulphuric anhydride, leaving a residue of alumina. AP(S0 4 ) 3 = 3S0 3 + APO 3 It is seen that aluminium sulphate represents 3 molecules of sulphuric acid, in which the 6 atoms of hydrogen have been replaced by the hexatomic couple AP. H 2 SOM (SO 4 H 2 S0 4 f- + APO 3 == 3H 2 -f (AP)* 1 SO* H 2 S0 4 ) (.SO 4 ALUMINIUM AND POTASSIUM DOUBLE SUL- PHATE, OR ALUM. A1 2 (SO 4 ) 3 .K 2 SO* -f 24H 2 O If a concentrated solution of aluminium sulphate be added to a concentrated solution of potassium sulphate, and the mix- ture be stirred with a glass rod, a crystalline deposit soon forms from the union of the two salts to form a double sulphate which is alum. This salt is not very soluble in cold water, but dissolves abundantly in boiling water, and is deposited on cooling in 316 ELEMENTS OP MODERN CHEMISTRY. voluminous, transparent octahedra. When heated, these crys- tals melt in. their water of crystallization (24 molecules), and in losing this water, the melted mass swells up considerably. Alum may be obtained crystallized in cubes, and it is prepared in this form in the neighborhood of Civita-Vecchia by working a mineral which contains the elements of alum with a large excess of alumina. The mineral is known as aluminite, and the cubical alum is called Roman alum. This cubical variety may be prepared in the laboratory by adding a small quantity of potassium carbonate to a hot solu- tion of ordinary alum, so that the precipitate first formed will be redissolved on agitating the liquid. On cooling, cubical crystals are deposited which are ordinarily opaque. These are formed under the influence of a small quantity of basic sul- phate (aluminium sulphate combined with an excess of alu- mina) contained in the liquid, and which probably enters into the constitution of the crystals. With this slight difference, octahedral alum and cubical alum present the same composi- tion, which is expressed by the formula A1 2 (S0 4 ) 3 .K 2 SO* -f 24H 2 0. Ammonia alum is obtained by adding ammonium sulphate to solution of aluminium sulphate. It possesses a constitution analogous to that of ordinary alum, with which it is isomor- phous. It contains AP(S0 4 ) 3 .(NH 4 ) 2 S0 4 -f 24H 2 It is often substituted in the arts for potassium alum, being cheaper than the latter. When strongly calcined, it leaves a residue of pure alumina. Other alums are known in which iron, manganese, and chro- mium play the part taken by aluminium in ordinary alum. These alums are all isomorphous (Mitseherlich). By the ac- tion of sulphuric acid on the sesquioxides of the above metals, sulphates are formed analogous to aluminium sulphate, and of which the composition is expressed by the general formula (R 2 ) vi (S0 4 ) 3 . With the sulphates M 2 S0 4 , they form alums, all of which crystallize in regular octahedra, and which can be mixed in one and the same crystal without the form of the latter being affected by the mixture. The following are the most important of these compounds: Manganese alum .... Mn2(SO*)3.R2SO* + 24IPO Iron alum Fe2(S0 4 ) 3 .R2SO* + 24H*0 Chromium alum .... Cr2(SO*J 3 .K2SO* + 24H 2 ALUM. 317 It is seen that each of these presents an atomic composition similar to that of ordinary alum. The aluminium compounds are widely disseminated in nature. Feldspar is a double silicate of aluminium and potassium. The latter metal is replaced by sodium in albite, and by calcium in labradorite. Many other minerals contain aluminium silicate combined with alkaline or earthy silicates : such are granite, idiocrase, mica, etc. The zeolites are silicates of aluminium containing water of crystallization. Clay is a hydrated silicate of aluminium ; it results from the disintegration of feldspar by the action of water and air, the alkaline silicate being gradually dissolved and eliminated. The purest clay is kaolin, or porcelain clay ; it contains alumina, silica, and water in the proportions indicated by the formula 2Si0 2 ,AP0 3 ,2H 2 0. Plastic clays are those which form a binding paste when mixed with water, and acquire great hardness after being baked, without fusing. They are used for the manufacture of pottery, refractory fire-bricks, and crucibles. Fuller's earth is a clay which forms with water a paste that is but slightly adhe- rent ; it is employed in scouring and fulling cloth. Marls are intimate mixtures of clay and chalk; they are employed in agriculture. Pottery. Clay is the basis of all pottery. Other matters, such as sand, powdered feldspar or quartz, etc., are generally added, for while they diminish the plasticity of the clay, they also diminish its shrinkage on baking. Pottery is classified as semi vitrified pottery, such as porcelain and stoneware ; porous pottery, such as faience and bisque; and common pottery or terra-cotta. Porcelains. These are manufactured from kaolin, to which sand is added to prevent shrinkage, and feldspar, which causes the ware to undergo a partial fusion, and renders it translucent. These materials are finely pulverized, mixed with water, and the paste is kneaded for a long time in order to render it homo- geneous. Pieces fashioned in this paste are submitted to a pre- liminary baking, which gives them a certain degree of coherence. The porous porcelain thus obtained must be coated with a var- nish which will melt and spread upon its surface : this glaze is 27* 318 ELEMENTS OF MODERN CHEMISTRY. formed of a mixture of quartz and kaolin reduced to an impal- pable powder ; the latter is suspended in water, into which the pieces are dipped. They are then subjected to a second baking in ovens where the temperature is sufficiently elevated to fuse the glaze and partially vitrify the paste. Ceramic Stonewares. These are manufactured from the same materials as porcelain, but less pure ; they are therefore slightly colored. They are baked at a high temperature, and are glazed by throwing common salt upon the incandescent objects in the furnace ; hydrochloric acid is disengaged, and a double silicate of aluminium and sodium is formed, which fuses and spreads upon the surface of the ware. Faiences are made from plastic clay mixed with quartz re- duced to an impalpable powder. Articles formed of this paste are submitted to a preliminary baking, and are then coated with a fusible glaze, composed of quartz, potassium carbonate, and oxide of lead. A second baking causes the pieces to become covered with an impermeable, vitreous layer of silicate of lead and potassium. This glaze is transparent ; for ordinary ware it is rendered opaque by the addition of oxide of tin. It is a true enamel. Common pottery, which serves for culinary purposes, is made from ferruginous clay, mixed with sand and marl. The glazing is composed of a double silicate of aluminium and lead. IRON. Fe(Ferrum) = 56 Natural State and Metallurgy. Iron is the most impor- tant of the metals. Its preparation and working are difficult, therefore it was not the first metal used by civilized man. The bronze age preceded the iron age, and those who first employed the latter metal probably extracted it from the masses which fall from time to time upon the surface of the earth, and are known as meteorites. Their principal constituent is metallic iron, which is alloyed with nickel, cobalt, and chromium. Iron is employed in three principal forms : soft or malleable iron, cast iron, and steel. Soft iron is almost pure iron ; cast iron is a combination of iron with carbon and silicon ; steel also contains carbon, but in smaller proportion than cast iron. The principal ores of iron are the magnetic, or black oxide, IRON. 319 Fe 3 4 , red hematite, Fe 2 3 , and spathic iron or ferrous carbon- ate, FeCO 3 . The various hydrates of the sesquioxide (oolitic iron, broivn hematite, etc.) and ferrous carbonate mixed with clay (bog-iron ore), are more abundant than the preceding, but are not as rich and are less valuable. All of these minerals are oxidized. If the ore contain sul- phur, that element is first driven out by roasting. The metal- lurgy of iron then consists in reducing the oxide with carbon, and separating the reduced iron from the earthy matter, which is generally silicious. Two methods are employed for this purpose. The first consists in heating the rich ores with charcoal alone ; part of the oxide of iron then combines with the gangue, forming a very fusible slag (double silicate of aluminium and iron). This is the Catalan method. The other consists in mixing the ore with coal and calcium carbon- ate ; the gangue then com- bines with the lime, forming a double silicate of lime and aluminium, which fuses only at a very high temperature. Under these conditions the iron unites with a portion of the carbon, forming cast iron. This is the blast-fur- nace method. Catalan Method. This is only applicable to very rich ores and in countries where combustibles are expensive, as in Spain, the Pyrenees, and in Corsica. Fig. 102 represents a sec- tion of a Catalan furnace ; it is a trough-shaped masonry furnace with a hearth. The F IG . 102. materials are placed in two piles, side by side, upon a layer of well-ignited charcoal ; one pile consists of charcoal and is next the tuyere ; the other is the ore, equal to half the quantity of charcoal, and is placed oppo- site. The combustion is sustained by the blast from a tuyere, D, which reaches the border of the hearth. The carbon dioxide here formed is converted into carbon monoxide by the 320 ELEMENTS OF MODERN CHEMISTRY. mass of incandescent charcoal, and the latter gas reduces the ore, again passing into the state of dioxide. Metallic iron is thus formed, and at the same time a portion of the ferric oxide is reduced to ferrous oxide, and combines with the gangue, forming a double, alumino-ferrous silicate, which is very fusible and constitutes the slag. The reduced iron collects in the bottom of the hearth in the form of a spongy mass, which is agglutinated and forged under the hammer. FIG. 103. Blast-furnace Process. All iron ores may be treated by this method. They are crushed and introduced with alternate layers of limestone and coal into the blast-furnace (Fig. 103). The latter has the form of two cones, the bases of which are IRON. 321 joined together. It is closed at the bottom, and hot air is in- jected through tuyeres to sustain the combustion. It is open at the top, where it is continually charged with fresh materials, as the incandescent mass sinks in the furnace and the molten mate- rials are drawn off below. The latter first collect in a cavity placed below the vent of the tuyere, and separate on this hearth into metal, which sinks to the bottom, and slag, which floats and flows over the edge. When the crucible is full of molten metal, the latter is run off into channels made in sand upon the floor of the casting-room. In these rough moulds it solidifies in bars having a semicircular section, which are called pigs. The reactions which take place in the blast-furnace are of great interest. At the lower part, where the temperature is the highest, carbon dioxide is produced by the combustion of the coal ; farther up, in the widest portion, this gas is reduced to carbon monoxide by the incandescent coal ; still higher, where the furnace begins again to contract, and where the temperature is dull red, the carbon monoxide reduces the oxide of iron, and a spongy mass of metallic iron is there formed. In descending, this iron unites with part of the carbon, and at the same time the silica of the gangue combines with the lime, forming a silicate which fuses and constitutes the slag. A small quantity of silica is reduced in the hottest part of the furnace, and the silicon formed combines with the cast iron. Cast iron is converted into soft iron by refining ; this opera- tion consists in removing from the cast iron the greater part of its carbon. For this purpose it is melted in contact with the air ; the carbon, silicon, and a small proportion of iron are oxidized, forming a basic silicate, of which the excess of oxide is finally reduced by the carbon of the cast iron. The latter thus becomes less fusible, and is converted into a spongy mass of soft iron. Several of these masses are united and the scoriae expressed from them by the blows of a steam-hammer. Or the metal is melted on the hearth of a reverberatory furnace under a layer of ferruginous scoriae and scales of oxide of iron ; the oxygen of these materials burns the carbon out of the cast iron, the whole mass being vigorously stirred. The latter operation is called puddling. Preparation of Pure Iron. Pure iron may be obtained by reducing ferric oxide by hydrogen at a temperature near red- ness, or by passing hydrogen over anhydrous ferrous chloride ' o* 322 ELEMENTS OF MODERN CHEMISTRY. contained in an incandescent porcelain tube. Hydrochloric acid is formed and evolved, and the iron remains as a gray, spongy mass, having a metallic lustre where it has been in contact with the porcelain (Peligot). Properties of Soft Iron. Forged, or bar iron, is not chem- ically pure. It contains a small quantity of carbon, and traces of silicon, sulphur, and phosphorus, and even nitrogen. The purest soft iron is that used for the teeth of carding-inachines and for piano-strings. The density of forged iron varies from 7.4 to 7.9. It is very tenacious, ductile, and malleable. When rolled out, it is called sheet iron. Tin plate is sheet iron covered with a layer of tin. Galvanized iron is coated with a surface of zinc. Iron melts only at the highest heats of a wind-furnace. When softened by a white heat, it may be soldered to itself, or welded, a very important property for the working of the metal. Iron is attracted by the magnet ; it is magnetic ; but it is not, like steel, capable of retaining magnetism when removed from the magnetic influence. It is not altered by dry air at ordinary temperatures, but at a red heat it absorbs oxygen and is converted into scales of black oxide of iron. Iron may be obtained as an impalpable powder by reducing finely-divided ferric oxide by a current of hydrogen at as low a temperature as possible. In this state it takes fire when ex- posed to the air at ordinary temperatures : it is pyrophoric. Iron rapidly becomes oxidized in moist air ; it becomes cov- ered with a layer of rust, which is ferric hydrate. It is con- sidered that the oxidation of iron moistened with water is first set up by the oxygen dissolved in the water; it continues with greater energy as soon as a light coat of ferric hydrate has been formed on the metal. The hydrate forms a voltaic couple with the iron itself, by which the water is decomposed ; part of the hydrogen displaced by the iron combines with the nitrogen of the air, forming ammonia; indeed, rust always contains a small proportion of ammonia. Iron decomposes water at a red heat, setting free the hydro- gen. It dissolves readily in hydrochloric acid, liberating impure and fetid hydrogen. Its oxidation by nitric acid is attended by curious phenomena. If dilute nitric acid be poured upon iron tacks, the metal is at once attacked with an abundant disengagement of red vapors. IRON. 323 On the other hand, the same metal is not attacked by very concentrated nitric acid (monohydrated), and after having been exposed to the strong acid, the tacks may be put into dilute acid, and the latter will then be found to have no effect. By the action of the concentrated acid, the iron becomes passive; its surface is covered with a thin layer of gas which protects it. But if it be touched at any point with a copper wire while in the dilute acid, chemical action will instantly be re-established. Cast Iron and Steel. The properties and appearance of cast iron differ with the proportions of carbon and silicon which it contains. The iron does not form definite compounds with these bodies; they seem to be dissolved by the cast iron when it is liquid. When cast iron containing much carbon is quickly cooled, it becomes hard, brittle, whiter than soft iron, and seems homogeneous. This is white iron. When slowly cooled, a large proportion of the carbon is deposited as laminae of graphite, and the less homogeneous iron then possesses a certain degree of malleability : it is gray iron. Some cast irons contain traces of sulphur and phosphorus; they remain white even after very slow cooling. Others are lamellar and glittering; they contain manganese and are rich in carbon. The proportion of carbon contained in cast iron varies from 2 to 5.5 per cent. Steel contains less carbon, from 0.7 to 2 per cent. The quantities of carbon contained in steel and even in cast iron render it difficult to suppose that these products are veritable carbides of iron. Steel may be obtained by a partial decarbonization of cast iron. Manganiferous iron is especially applicable for this prep- aration. It is submitted to a partial refining, being maintained in the liquid state for some hours under a layer of scoriae rich in oxide of iron. A part of the carbon is burned out by the oxygen of this oxide : natural steel is thus obtained. Soft iron may be converted into steel. The operation is con- ducted in cases of refractory fire-clay, into which bars of iron, and charcoal-powder, mixed with a small quantity of ashes and common salt, are introduced in alternate layers. The bars being thus isolated in a bed of charcoal, the cases are closed and heated to redness in a furnace. The incandescent metal absorbs carbon, and at the termination of the operation is found con- verted into steel by cementation. 324 ELEMENTS OF MODERN CHEMISTRY. The most homogeneous and most valuable steel is cast steel. It is obtained by fusing crude steel in crucibles in a wind-fur- nace. Bessemer has introduced an important improvement in the manufacture of steel. His process, which bears his name, con- sists in adding variable quantities of a properly-constituted cast iron to molten and perfectly refined soft iron. In this process, the iron to be converted into steel is decar- bonized by a current of air which is forced through the molten metal by strong press- ure. The operation is conducted in an appa- ratus represented in Fig. 104, which is called the converter. It has an ovoid form, is constructed of strong plate iron, and is well- lined with refractory fire-bricks. It is ar- ranged on trunnions, so that an oscillating move- ment may be given to it. The air arrives under pressure by the tuyeres which open into the bot- tom of the converter. T? 16 latter is first filled with incandescent coke, which is brought into active combustion by the blast. When the interior of the converter is heated to whiteness, the coke is emptied out and replaced by the molten cast iron, the con- verter being inclined to prevent the entrance of the metal into the tuyeres. The blast is then again turned on, and the com- pressed air bubbling through the molten metal burns out all of the carbon. A flame of great brilliancy rushes from the orifice of the apparatus, and the aspect of this flame indicates precisely the progress of the operation and its termination. At this moment the apparatus is inclined, the blast arrested, and a sufficient quantity of melted cast iron or spiegeleisen, a crystalline cast iron rich in carbon, is added to the now refined iron to convert the whole into steel ; about 7 per cent, of spie- OXIDES OF IRON. 325 geleisen is required. The steel is then run out into suitable moulds. The valuable qualities of steel are well known. It is suscep- tible of a high polish ; it is ductile and malleable like iron, and can also be forged. At the temperature at which malleable iron becomes soft, steel melts. It becomes hard and brittle when it is suddenly cooled after having been heated to redness. This operation, which is called tempering, develops new quali- ties in the steel, elasticity and hardness. It assumes these properties in different degrees, according to the rapidity of the cooling, and the difference between the temperature to which it has been heated and that to which it is cooled. The greater this difference, and the more rapid the cooling, the harder will the steel become. After a slow cooling, it is soft and mallea- ble like iron. When tempered steel is heated, and allowed to cool slowly, it partly or entirely loses its hardness. It loses it entirely if it be heated to the temperature to which it was exposed before tempering. Its temper is drawn incompletely, that is, it re- tains a certain amount of hardness and elasticity, if it be re- heated to inferior temperatures. The qualities which it will assume after cooling may be predicted from the various tints developed on its surface during the heating. Each of these tints corresponds to a determined temperature. Straw-yellow corresponds to 220 Brown " 255 Light blue " 285-290 Jn.ligo-blue " 295 Sea-green " 331 OXIDES OF IRON. Three oxides of iron are known : Ferrous oxide FeO Ferric oxide Fe 2 O 3 Ferroso-ferric oxide . Fe 3 O 4 Fremy has also discovered the existence of a ferric acid, of which the composition is not certainly established. Ferrous Oxide, FeO. Debray has obtained this oxide by partially reducing ferric oxide. The latter is heated in a cur- rent of gas formed of equal volumes of carbon monoxide and carbon dioxide. A black powder remains, which is ferrous oxide. Fe 2 3 + CO = 2FeO -f CO 2 28 326 ELEMENTS OF MODERN CHEMISTRY. Ferric Oxide, Fe 2 3 . This is found anhydrous in nature in red hematite and specular iron. It may be prepared by calcining ferrous sulphate, or green vitriol. This salt first loses its water, and then at a red heat decomposes into sul- phuric anhydride, sulphurous oxide, and ferric oxide. 2FeS0 4 = SO 3 + SO 2 + Fe 2 3 A red powder is thus obtained, which is known as colcothar, or jeweller's rouge. This oxide is amorphous, while red hematite is crystallized in acute rhombohedra. H. Deville has succeeded in converting the amorphous oxide into the crystallized by heating the former to redness in a very slow current of hydrochloric acid. Rust is ferric hydrate, a combination of ferric oxide with water, and ordinarily presents the composition 2Fe 2 3 -f 3H 2 Such a hydrate is also encountered in nature as brown hematite. Another natural hydrate, containing Fe 2 3 -j- IPO, is known under the name of gcethite. Ammonia or potassium hydrate will at once produce a volu- minous and flocculent, rust-colored precipitate in a solution of ferric chloride. This precipitate constitutes a ferric hydrate. But if an excess of tartaric acid be added to the solution of a ferric salt, the liquid may be saturated with potassium hy- drate and will still remain clear, no precipitate of ferric hydrate being formed. Advantage is taken of this property in analysis for the sepa- ration of ferric oxide from other oxides which tartaric acid does not retain in solution in an alkaline liquid. If a solution of ferric acetate be poured into a dialyser (page 199), and the water in the exterior vessel be frequently changed, the salt will finally be entirely decomposed. Acetic acid will pass through the membrane, while ferric hydrate will remain dissolved in the water in the dialyser (Graham). Ferroso-ferric Oxide, Fe 3 4 . This compound, also called magnetic oxide of iron, constitutes the black scales which form upon the surface of iron when it is heated to redness in the air ; it may be regarded as a compound of ferrous and ferric oxides. FeO Fe 2 3 = Fe 3 4 . SULPHIDES OF IRON CHLORIDES OP IRON. 327 SULPHIDES OF IRON. Several sulphides of iron are known. The disulphide, or pyrites, FeS 2 , a largely-diffused mineral, is the most important of these sulphides. It occurs in two distinct forms : Yellow pyrites, which crystallizes in cubes. It occurs as brilliant cubes, or dodecahedra, having a yellow color and a metallic lustre. White pyrites, which forms rhombic prisms, variously modi- fied, and presents a dull, greenish-yellow color. This variety is much more alterable than the other, and possesses a great tendency to attract oxygen from the air and become converted into sulphate. When heated in closed vessels, pyrites loses a part of its sulphur. A combination of monosulphide and sesquisulphide of iron is encountered in nature ; it crystallizes in regular hexagonal prisms and is called magnetic pyrites. Monosulphide of Iron, FeS, is found in small quantity in many meteorites. It is ordinarily obtained by heating to red- ness in a covered crucible a mixture of three parts of iron- filings and two parts of sulphur. When the mixture has fused, it is poured out and solidifies to a brittle, blackish mass, having a metallic reflection. In this state, it is used for the preparation of hydrogen sulphide. CHLORIDES OF IRON. Ferrous Chloride, Fed 2 , is obtained anhydrous by the action of dry hydrochloric acid gas upon metallic iron. It forms white pearly scales. When iron is treated with aqueous hydrochloric acid, it dissolves, and hydrogen is disengaged. The green, filtered liquid deposits, when sufficiently concentrated, bluish- green, oblique rhombic prisms. This is hydrated ferrous chlo- ride, Fed 2 -f 4H 2 O. Ferric Chloride, Fe 2 Cl 6 , is formed when a current of chlorine is passed over iron-turnings heated in a glass or porcelain tube. The two bodies combine with incandescence, and if the chlorine be in excess, ferric chloride will be obtained as a brilliant black, crystalline sublimate. 328 ELEMENTS OF MODERN CHEMISTRY. This body is very soluble in water and forms a yellow-brown solution. The latter may be obtained by dissolving ferric oxide, such as powdered hematite, in hot hydrochloric acid, or by passing chlorine into a solution of ferrous chloride. Ferric chloride is also soluble in alcohol. FERROUS SULPHATE. 7H 2 O This salt has long been known under the names green vitriol and copperas. It is obtained by exposing iron pyrites to the air, or roasting that mineral at a moderate heat. It is generally prepared by dissolving iron in dilute sulphuric acid, and it is a residue from the preparation of hydrogen sulphide by means of iron sulphide and dilute sulphuric acid. It crystallizes in oblique rhombic prisms, containing 7 mol- ecules of water of crystallization. When exposed to the air, these crystals effloresce slightly, and at the same time their surface becomes yellow from absorption of oxygen and the formation of ferric subsulphate. 2FeS0 4 + = Fe 2 0(SO) 2 = Fe 2 3 .2S0 3 When heated, they lose their water, of which six molecules are disengaged at 114, and the seventh only at 300. At a higher temperature the salt decomposes into sulphurous oxide, and a ferric subsulphate different from the preceding. 2FeSO == SO 2 + (Fe 2 O 2 )SO* The crystals of ferrous sulphate are freely soluble in water. 100 parts of the salt dissolve in 164 parts of water at 10, and in 30 parts of boiling water. The green solution absorbs oxy- gen from the air, becomes troubled, and deposits yellow ferric subsulphate. Other hydrates of ferrous sulphate are known. According to Mitscherlich, a saturated boiling solution of the salt deposits at 80 crystals containing four molecules of water. According to Marignac, when a solution of ferrous sulphate containing free sulphuric acid is evaporated in a vacuum, crystals are first deposited which contain 7 molecules of water, then a sulphate FeSO 4 -f 5H 2 0, and finally, FeSO 4 + 4H 2 0. The sulphate FeSO 4 -f- 5H 2 0, is isomorphous with crystal- lized cupric sulphate (blue vitriol), and like it crystallizes in dissymetric prisms. FERRIC SULPHATE FERROUS CARBONATE. 329 FERRIC SULPHATE. Fe 2 (SO) 3 This salt is obtained by heating ferrous sulphate with nitric and sulphuric acids ; the brown solution is evaporated, and the residue well dried. 2FeS0 4 -f H 2 S0 4 -f = H 2 + Fe 2 (S0 4 ) 3 Ferric sulphate is a slightly -yellowish, white mass, which dissolves completely, but very slowly, in water. The solution is yellow-brown, and has an acid reaction. When concentrated by evaporation, it deposits a deliquescent, yellowish, crystalline mass, which constitutes hydrated ferric sulphate. There are several ferric subsulphates ; those which have been mentioned above result from the action of one molecule of ferric oxide upon one or two molecules of sulphuric acid, the neutral sulphate resulting from the action of one molecule of ferric oxide upon three molecules of sulphuric acid. IFSO 4 4- Fe 2 3 = H 2 + (Fe 2 2 )"SO 4 Ferric monosulphate. Ferric disulphate. H 2 S0 4 ( SO 4 H 2 SO 4 + Fe 2 3 = 3H 2 + (Fe 2 / 1 3 SO 4 H'SO* ( SO 4 Ferric trisnlphate (normal sulphate). FERROUS CARBONATE. FeCO 3 Spathic iron ore, which crystallizes in rhombohedra, is fer- rous carbonate. When a solution of sodium carbonate is added to a solution of ferrous sulphate, a greenish-white precipitate is obtained, which rapidly becomes colored in the air, absorb- ing oxygen and losing carbonic acid. When recently precipi- tated, it dissolves in a large excess of carbonic acid. Characters of Ferrous Salts. The solutions of these salts are green j they are not precipitated by hydrogen sulphide, but ammonium sulphide forms a black precipitate of ferrous sul- 28* 330 ELEMENTS OF MODERN CHEMISTRY. phide. Potassium hydrate or ammonia produces a greenish- white precipitate of ferrous hydrate, insoluble in an excess of the reagent, and rapidly becoming colored in the air. Potas- sium ferrocyanide (yellow prussiate of potash) forms with fer- rous salts a light-blue precipitate. Potassium ferricyanide (red prussiate) forms a dark-blue precipitate. Solution of gall-nuts does not color ferrous salts. Characters of Ferric Salts. Hydrogen sulphide produces a precipitate of sulphur, reducing the salts to the ferrous state. Ammonium sulphide precipitates them black. Potassium hy- drate and ammonia form red-brown precipitates of ferric hy- drate, insoluble in an excess of the reagent. Potassium ferro- cyanide forms a dark-blue precipitate which is Prussian blue. Potassium ferricyanide produces a dark-brown color without precipitation. Potassium sulphocyanate gives a blood-red color. Solution of gall-nuts forms a bluish-black precipitate which constitutes ink. ZINC. Zn = 65.2 Treatment of Zinc Ores. The zinc ores which are worked are calamine and blende. Calamine is carbonate of zinc, often mixed with silicate ; it contains also oxide of iron. Blende is sulphide of zinc; it frequently contains a small quantity of ferrous sulphide, which gives it a brown color, more or less intense. Zinc ores are abundant in England, Silesia, Belgium, and throughout the United States. They are generally accom- panied by other minerals; thus, blende is often mixed with pyrites and galena (lead sulphide). The ore is then first sub- mitted to an ingenious system of washing, by which the various sulphides separate from each other by reason of their different densities. In order to extract the zinc from blende separated by this method, or from calamine, the minerals are first roasted. By the action of heat calamine loses carbonic acid gas and water, and the blende disengages sulphurous oxide and is converted into zinc oxide. Thus converted into oxide, and rendered more friable by the heat, the zinc ores are pulverized and calcined with charcoal. Carbon monoxide is disengaged, and the zinc set at liberty volatilizes, and is condensed in suitable recipients. ZINC. 331 The operation is conducted in cylinders of refractory clay, a number of which are arranged in a furnace, and their open extremities connected with conical recipients of galvanized iron (Fig. 105). In Silesia, these cylindrical retorts are replaced by muffles, which are heated in a furnace and communicate with recipients placed outside (Fig. 106). FIG. 105. FIG. 106. In England, the reduction of the roasted ore is accomplished in crucibles, through the bottoms of which pass vertical tubes which terminate in a reservoir below the furnace. The zinc vapors first rise and then descend by the tube, and as they condense, the melted metal flows into the recipient. The operation is called distillation per descensum (Fig. 107). The zinc of commerce is not always pure, especially when it occurs in masses ; it contains small quantities of iron, copper, lead, cadmium, carbon, and arsenic. Sheet zinc is generally less impure. Zinc may be purified by melting it several times with small quantities of nitre. Properties. Zinc has a bluish-, white color; its density varies from 6.86 to 7.2, according as FIG. 107. 332 ELEMENTS OF MODERN CHEMISTRY. it has been melted or rolled ; its fracture is laminated and bril- liant. Commercial zinc is brittle at ordinary temperatures ; it becomes malleable at a few degrees above 0, but when heated to 200 it again becomes brittle. It melts at 410, and distils at about 1000 (H. Deville and Troost). Its surface soon tarnishes in moist air, but the oxidation is only superficial. It is due to the formation of a hydrocarbonate of zinc, which covers the metal with an impermeable surface and protects it from further oxidation. When heated to redness in contact with the air, zinc vola- tilizes and burns with a greenish flame, being converted into oxide, which rises as smoke and falls in very light, white flakes, formerly called flowers of zinc or philosopher's wool. Zinc dissolves with evolution of hydrogen in hydrochloric and sulphuric acids, and in boiling solutions of potassium and sodium hydrates. When perfectly pure, it is dissolved with difficulty by dilute sulphuric acid at ordinary temperatures, and the easy solubility of the metal of commerce must be attrib- uted to the presence of small quantities of foreign metals. The latter being electro-negative in contact with zinc, form voltaic couples, in which the zinc is the more oxidizable metal. Galvanized iron is iron covered with a thin layer of zinc; it is prepared by plunging carefully-cleaned iron objects into a bath of molten zinc. Brass is an alloy of copper and zinc, obtained by melting the two metals together in crucibles. ZINC OXIDE. ZnO This oxide is prepared in the arts by heating zinc in large muffles ; the product is separated from traces of metallic zinc by suspending it in water and rapidly decanting the white liquid. The zinc sinks to the bottom of the vessel before the lighter white powder has time to deposit ; the latter is therefore carried by the water into a second vessel, where it is allowed to settle. The process is called elutriation. Oxide of zinc is white ; it is irreducible by heat and is insolu- ble in water. A hydrate of this oxide is precipitated when an alkali is added to the solution of a zinc salt. ZnSO 4 + 2KOH = K 2 S0 4 -f Zn(OH) 2 Ziuc sulphate. Zinc hydrate. ZINC SULPHIDE ZINC CHLORIDE. 333 An excess of alkali will redissolve the precipitate. Zinc oxide is largely used in the arts as a substitute for white lead as a pigment. ZINC SULPHIDE. ZnS The blende which occurs in nature is sulphide of zinc. It crystallizes generally in regular octahedra, sometimes in double pyramids of six faces (Friedel). On adding an alkaline sulphide to a neutral solution of a zinc salt a white precipitate is obtained, which is hydrated zinc sulphide. When moderately heated in contact with the air, zinc sul- phide absorbs four atoms of oxygen and is converted into sul- phate. At a very high temperature it is converted into oxide, with formation of sulphurous oxide. ZINC CHLORIDE. ZnCl 2 Zinc reduced to thin sheets will burn in chlorine. Zinc chloride is prepared in the laboratory by dissolving zinc in hydrochloric acid. The aqueous solution, evaporated to a syrupy consistence, deposits a hydrated chloride, ZnCl 2 -f- H 2 0, crystallizing in deliquescent octahedra. This salt loses its water when strongly heated, and melts at about 250. On cooling, a solid white mass is obtained, which is the anhydrous chloride ; in this state it is very avid of water and deliquesces when exposed to the air. It volatilizes without decomposition at a red heat. It is very soluble in water, and dissolves also in alcohol. ZINC SULPHATE. ZnSO 4 + 7H 2 O This salt was formerly known as white vitriol. It is ob- tained by moderately roasting blende. The latter being often mixed with pyrites, zinc sulphate and ferrous sulphate are formed, and when the product of the roasting is lixiviated a solution of the two salts is obtained. The solution is evapo- 334 ELEMENTS OP MODERN CHEMISTRY. rated, and the dry residue moderately calcined. The ferrous sulphate decomposes, yielding sulphuric acid, which distils, and ferric oxide, which remains mixed with the zinc sulphate. The residue being exhausted with water, the zinc sulphate dissolves and is deposited in crystals on the cooling of the concentrated solution. The salt may be prepared in the laboratory by dissolving zinc in dilute sulphuric acid : it is the residue in the prepara- tion of hydrogen. Sulphate of zinc crystallizes with 7 molecules of water. In this state it occurs as right rhombic prisms, isomorphous with magnesium sulphate. When heated, it melts in its water of crystallization, of which it loses 6 molecules ; the seventh it abandons only at 238. At a high red heat it is decomposed into zinc oxide, sul- phurous oxide, and oxygen. Zinc sulphate is very soluble in water, of which 100 parts dissolve 48.36 parts of the anhydrous salt at 10, and 95.6 parts at 100. The solution has a styptic taste. Zinc sulphate forms crystallizable double salts with the alka- line sulphates ; thus, there is a double sulphate of zinc and potassium, containing ZnS0 4 .K 2 SO* + 6H 2 Characters of Zinc Salts. The zinc salts are colorless unless the corresponding acid be colored. Their neutral solu- tions are partially decomposed by hydrogen sulphide, which precipitates white sulphide of zinc ; the addition of a mineral acid prevents the precipitation ; the zinc salts of organic acids, such as the acetate and lactate, are completely decomposed by hydrogen sulphide. Ammonium sulphide produces a white precipitate of sul- phide; this reaction is characteristic. Potassium and sodium hydrates, and also ammonia, form white precipitates, soluble in an excess of the reagent. Potassium ferrocyanide gives a white precipitate. GALLIUM. 335 GALLIUM. Ga = 69.9 This metal was discovered in 1876 by Lecoq de Boisbaudran. It is contained in small quantity in certain blendes. One of the richest, found in Westphalia, contains only one sixty-thou- sandth of its weight. In order to extract the gallium, the ore is roasted, and the product dissolved in sulphuric acid. An acid liquor is thus obtained, containing principally sulphate of zinc, with sulphates of iron, aluminium, indium, etc., and a trace of gallium sul- phate. The following reactions are employed by Lecoq de Bois- baudran and Jungfleisch for the separation of the gallium : 1. When the liquid is neutralized, the ferric oxide, alumina, and gallium oxide, which is a sesquioxide, are precipitated. The precipitate is redissolved in sulphuric acid, and the same operation repeated after converting the ferric oxide into ferrous oxide, which remains dissolved in the neutral liquid. By this means the greater part of the iron is removed. 2. Gallium oxide dissolves, like alumina and zinc oxide, in an excess of potassium hydrate ; when this solution is saturated with hydrogen sulphide, the zinc is precipitated as sulphide, while the gallium and aluminium remain in solution. The greater part of the zinc is thus separated. 3. When water is added to a boiling solution of gallium sulphate, the latter is precipitated as subsulphate, while alumi- nium sulphate remains in solution. 4. Gallium oxide dissolves in an excess of ammonia ; alumina does not. 5. Gallium separates in the metallic state when a voltaic current is passed through an alkaline solution of gallium oxide. Physical Properties. Gallium has a metallic lustre recalling that of nickel. It readily crystallizes in forms derived from a right rhombic octahedron, generally in magnificent laminae. Its density is 5.96. It melts at 29.5, and has a tendency to re- main in a state of superfusion. It is not volatile. This collection of properties gives to gallium a special place among the metals. It is one of the most remarkable of recent discoveries. Chemical Properties. These are but little known at present. 336 ELEMENTS OF MODERN CHEMISTRY. Gallium is oxidized but little, if at all, when heated in the air or in oxygen. It forms a sesqjiioxide, Ga*0 3 , which resembles alumina in that it forms alums. Gallium alum was obtained by Lecoq de Boisbaudran. Gallium combines directly with chlorine, forming a solid, crystalline, and very volatile chloride. INDIUM. In == 113.4 This metal was discovered in 1863 by Beich and Kichter in the zinc blendes of Freiberg (Saxony). It appears to exist in the majority of zinc blendes, and accompanies the zinc which is extracted from those minerals. It is ordinarily obtained from metallic zinc, which, however, contains only very small quantities of it. Commercial zinc (that of Freiberg is prefer- able) is digested in a quantity of dilute sulphuric acid insuffi- cient to dissolve all of the metal ; after several weeks, a spongy mass remains, which contains an excess of zinc and, indepen- dently of other metals, a small quantity of indium. This is the residue from which indium is obtained by processes which need not be here described. Indium is a brilliant metal, possessing almost the lustre of silver. It is soft and ductile. It melts at 176, and is vola- tile, but less so than zinc and cadmium. It approaches these metals in its general chemical properties, but is more electro- negative, both of the latter metals precipitating it from its solutions. Indium is characterized by several spectroscopic lines, among which are a very brilliant blue and a less marked violet line. Winkler has indicated two other less distinct blue lines. Two oxides of indium have been described, a sesquioxide, In 2 3 . and a suboxide. The first is obtained by calcining the nitrate ; it is yellow. When heated to 300 in a current of hydrogen, it is partially reduced, yielding a black suboxide. Indium chloride, In 2 Cl 6 , is formed when indium is heated in a current of chlorine. It is a snow-white, volatile solid. CADMIUM. 337 CADMIUM. Cd = 112 Natural State and Extraction, Cadmium is generally found associated with zinc, either as oxide in calamine, or as sulphide in zinc blende. As it is more volatile than zinc, it becomes concentrated in the first products of distillation. It is found especially, in the state of oxide, in the brown powder called cadmies, which condenses during the first hours of the distillation in the sheet-iron receivers adapted to the re- torts (Fig. 105). When mixed with powdered charcoal and calcined, this powder yields an alloy of zinc and cadmium which distils. The cadmium is extracted by dissolving the alloy in dilute sulphuric acid and passing a current of hydrogen sulphide through the acid liquid. The cadmium is precipitated as a yellow sulphide. This sulphide is dissolved in hydrochloric acid and the solution of cadmium chloride precipitated by am- monium carbonate. The cadmium carbonate thus obtained is calcined, and so converted into oxide, which is mixed with one-tenth its weight of powdered charcoal and heated in a clay retort. The cadmium distils. Properties. Pure cadmium has a white lustre, but soon tarnishes in the air. Its density is 8.60-8.69. It melts at 320 (Person), and boils at 860 (H. Deville and Troost). It may be obtained crystallized in octahedra. It dissolves in dilute sulphuric and hydrochloric acids with evolution of hydrogen. Cadmium Oxide, CdO. The oxide of cadmium may be ob- tained by calcining either the carbonate or nitrate. It has a yellowish-brown color, or a brown more or less deep. It is re- duced at high temperatures by carbon and by hydrogen, its reduction taking place more readily than that of zinc oxide. Cadmium Sulphide, CdS. This sulphide occurs in nature in the form of bright yellow, hexagonal prisms, terminated by six-sided pyramids. It may be prepared in the laboratory by precipitating a solu- tion of a cadmium salt by hydrogen sulphide or a soluble sul- phide. An amorphous precipitate of a fine yellow color is thus obtained. In this form it is employed in oil painting. Cadmium Iodide, CdP. This salt is prepared by digesting p 29 338 ELEMENTS OF MODERN CHEMISTRY. finely-divided cadmium with iodine in presence of water. It crystallizes from its aqueous solution in transparent and color- less, hexagonal prisms having a brilliant lustre. It is soluble in water and alcohol. Cadmium Sulphate, CdSO 4 -f 4H 2 0. Cadmium sulphate is obtained by dissolving the metal, or its oxide or carbonate, in dilute sulphuric acid. The neutral and concentrated solution deposits the salt in beautiful, right rectangular prisms. These crystals are efflorescent. COBALT. Co = 59 Cobalt was discovered by Brandt in 1753. It is found prin- cipally in the state of arsenide, CoAs 2 , and as sulph-arsenide, CoAsS (gray cobalt). Its ores are worked principally for the production of a dark-blue, vitreous mass, a combination of cobalt silicate and potassium silicate, known as smalt or azure blue. The metal is prepared in the laboratory by calcining its oxa- late in a covered crucible. CoC 2 0* = Co + 2C0 2 Cobalt oxalate. Carbon dioxide. It may be obtained as a metallic button by heating the pul- verulent metal in a lime crucible in a wind-furnace. The lime crucible is placed in another crucible of refractory clay, and the space between the two is filled up with fragments of quick- lime (H. Sainte-Claire Deville). Pure cobalt is silvery-white. It is very malleable ; its den- sity is 8.6, and it is magnetic. At ordinary temperatures it is unaffected by the air, but at a red heat it is converted into oxide. Oxides of Cobalt. A monoxide, CoO, and a sesquioxide, Co 2 3 , are known, and several intermediate oxides. The monoxide may be obtained by calcining cobalt carbonate in close vessels. It is a greenish-gray or olive-green powder, which is reduced by hydrogen, charcoal, and carbon monoxide at a red heat. When heated with borax before the blow-pipe, it dissolves, forming a blue glass. It is used for giving a blue color to glass and porcelain. COBALT. 339 When an excess of potassium hydrate is added to the solu- tion of a salt of cobalt, a rose-red precipitate of cobalt hydrate, Co(OH) 2 , is formed. Cobalt sesquioxide, Co 2 3 , is prepared by passing a current of chlorine through water, holding in suspension the rose- colored hydrate above mentioned. 2CoO + H 2 -f CP = Co 2 3 + 2HC1 The sesquioxide is deposited as a black powder, which may be dried by carefully heating it. Cobalt Chloride, CoCl 2 . When pulverulent cobalt is heated in a current of chlorine, it takes fire and is converted into a chloride, which sublimes in blue scales. A solution of this chloride may be obtained by dissolving either monoxide or car- bonate of cobalt in hydrochloric acid. The neutral solution is currant-red, and on evaporation deposits hydrated crystals of the same color. But when it is concentrated, after having added hydrochloric or sulphuric acid, it becomes blue. This change of color, due to the formation of anhydrous chloride even in the midst of the hot liquid, has caused the employ- ment of cobalt chloride as a sympathetic ink. Characters traced with the dilute solution, which is rose-colored, are invisi- ble on white paper, and appear blue only when the paper is warmed, again becoming invisible on cooling, by the absorption of atmospheric moisture. Cobalt Sulphate, CoSO 4 -f 7H 2 0. This salt is found in nature, crystallized in oblique rhombic prisms. It may be ob- tained by dissolving the oxide or carbonate in dilute sulphuric acid and concentrating the red solution. At ordinary temper- atures, the latter deposits red crystals, isomorphous with ferrous sulphate. Between 20 and 30, it yields right rhombic prisms, containing 6 molecules of water, and isomorphous with magne- sium sulphate. Characters of Cobalt Salts. The cobaltous salts are the more important. Their solutions are rose or currant-red, but when concentrated and hot they become blue, especially when an excess of acid is present. Hydrogen sulphide does not pre- cipitate solutions of cobalt salts. Ammonium sulphide forms a black precipitate. Potassium hydrate gives a blue precipitate of a basic salt, which, in presence of an excess of potassa, is converted into hydrate of cobalt, having a dirty rose color. 340 ELEMENTS OF MODERN CHEMISTRY. Ammonia forms a blue precipitate, soluble in an excess of the reagent. When heated with borax in the blow-pipe flame, the salts of cobalt yield beads of a pure blue color. NICKEL. Ni = 59 This metal was discovered by Cronstedt in 1751. Natural State and Extraction. Nickel is found as arsen- ide, NiAs 2 , in kupfernickel or nickeline. In the preparation of smalt from the ores of cobalt, which always contain nickel, the latter metal combines with the arsenic and a certain proportion of sulphur, forming a metallic-looking mass known as speiss. In the arts, nickel is extracted from kupfernickel or from speiss. In the laboratory it is prepared by reducing the oxide in a brasqued crucible, or by calcining the oxalate out of con- tact with the air. When heated to whiteness in a lime cruci- ble the nickel melts to a metallic button. Properties. Pure nickel is grayish-white. It is malleable, ductile, and very tenacious. Its density is 8.279, and may be increased to 8.666 by hammering. Next to manganese, it is the hardest of the metals. It is less fusible than iron and more fusible than manganese. It is magnetic at ordinary tempera- tures, but loses this property at about 250. It is unaltered by the air at ordinary temperatures, but absorbs oxygen at a red heat. It dissolves slowly in dilute sulphuric and hydrochloric acids, rapidly in nitric acid. In contact with concentrated nitric acid it becomes passive like iron. Nickel is used in the arts, in the manufacture of an alloy known as German silver, which contains 50 per cent, of copper, 25 of nickel, and 25 of zinc. Nickel may be deposited as a brilliant metallic layer by the electrolysis of a solution of nickel and ammonium double sul- phate (A. C. and E. Becquerel). Adams made an application of this property to the nickel-plating of various objects by electro-metallurgy, and the process is now largely employed. Oxides of Nickel. A monoxide, NiO, and a sesquioxide, Ni 2 3 , are known. The anhydrous monoxide is an ash-gray powder. It is obtained by strongly calcining the nitrate or carbonate. On NICKEL. 341 adding potassium hydrate to a nickel salt, an apple-green pre- cipitate of nickel hydrate, Ni(OH) 2 , is formed. Nickel sesquioxide may be obtained by moderately calcining the nitrate. It is black. When chlorine gas is passed into water holding nickel hydrate in suspension, a dark-brown pow- der is obtained, which is a hydrate of the sesquioxide. This hydrate may also be made by precipitating a nickel salt with potassium hydrate mixed with an alkaline hypochlorite. When strongly calcined, nickel sesquioxide abandons part of its oxygen and is changed into monoxide. Treated with hydro- chloric acid, it yields nickel chloride, and chlorine is disengaged. Ni 2 3 + 6HC1 = 2NiCl 2 + 3H 2 + Cl 2 Nickel Chloride, NiCl 2 . This salt may be obtained anhy- drous by the action of chlorine on nickel-filings ; it is volatile at a dull-red heat, and sublimes in golden-yellow scales. The hydrated chloride is formed by the action of boiling water on the anhydrous salt, or by the action of hydrochloric acid on the oxide or carbonate. Its solution is green, and after proper concentration deposits beautiful green crystals which contain NiCl 2 4- 9H 2 O. Nickel Sulphate, NiSO -}- 7H 2 0. The sulphate is depos- ited in fine, emerald-green, orthorhombic prisms, isomorphous with magnesium sulphate, when its solution is allowed to evap- orate spontaneously below 15. There is another hydrate con- taining 6H 2 0, which is dimorphous. When deposited between 20 and 30, it crystallizes in square octahedra, but when its solution is made to crystallize between 60 and 70, right rhom- bic prisms are obtained, isomorphous with the corresponding sulphates of magnesium, zinc, and cobalt. Nickel sulphate dissolves in 3 times its weight of water at 10. Characters of Nickel Salts. The nickel salts when hy- drated or in solution have a fine emerald-green color. When anhydrous they are yellow. Hydrogen sulphide does not precipitate them from acid solu- tions. Ammonium sulphide throws down a black precipitate. Potassium hydrate and potassium carbonate form apple-green precipitates. In neutral solutions, ammonia gives a green precipitate of nickel hydrate, which dissolves in an excess of ammonia, form- ing a blue solution. 29* 342 ELEMENTS OF MODERN CHEMISTRY. MANGANESE. Mn = 55 This metal has been obtained as a coherent, very hard mass, by reduction of either manganous carbonate or red oxide of manganese with charcoal or sugar in a lime crucible at the highest heat of a wind-furnace (H. Deville). It is whitish-gray, and almost as infusible as platinum. Its density is 7.2. Its powder decomposes warm water. MANGANESE OXIDES. Manganese forms six compounds with oxygen : Manganous oxide MnO Manganoso-manganic oxide Mn 8 0* Manganic oxide Mn 2 3 Manganese dioxide MnO 2 Manganic anhydride MnO 3 Permanganic anhydride Mn 2 7 Manganous oxide is formed when manganous carbonate is strongly heated in a current of hydrogen. Carbon dioxide is evolved, and a green powder, which is manganous oxide, re- mains, It takes fire on contact with an incandescent body, and is converted into a brownish-red powder, which is red oxide of manganese, 3MnO + = Mn 3 O The latter body is also formed by the calcination of the diox- ide. It is analogous to the magnetic oxide of iron, and con- stitutes the mineral known as hausmannite. Manganic oxide, Mn 2 8 , occurs in nature in the crystallized state as braunite. It is isomorphous with alumina and ferric oxide. MANGANESE DIOXIDE. (BINOXIDE OR PEROXIDE OF MANGANESE.) MnO 2 This important body is found abundantly in nature ; it con- stitutes the mineral pyrolusite. It may be obtained pure and anhydrous by exposing a concentrated solution of manganous nitrate to heat and gradually raising the temperature to 155. MANGANIC ACID. 343 Nitrous vapors are evolved, and a brilliant brown-black mass is obtained, which is the dioxide. Mn(N0 3 ) 2 = MnO 2 + 2N0 2 It loses one-third of its oxygen when heated to redness, and is converted into the red oxide. When heated with concen- trated sulphuric acid, it loses half of its oxygen, manganous sulphate being formed, MnO 2 + H 2 S0 4 = MnSO 4 + H 2 + O With hydrochloric acid it yields water, chlorine, and manga- nous chloride. A hydrate of manganese dioxide is formed when an excess of chlorine is directed into water holding in suspension man- ganous hydrate or carbonate. This hydrate is a dark-brown powder. Manganese dioxide is largely employed for the preparation of oxygen and chlorine. It is used to decolorize glass black- ened by carbonaceous matters or rendered green by a trace of iron. MANGANIC ACID. When manganese dioxide is heated with potassium hydrate in a silver crucible, and the calcined mass is exhausted with water, the latter dissolves out potassium manganate. A dark- green liquor is thus obtained which, when evaporated in vacuo, deposits a crystalline mass. These crystals may be drained on a porous porcelain plate, and green needles of potassium man- ganate, K 2 MnO*, remain. The salt is isomorphous with the sulphate K 2 S0 4 . When the green solution is boiled, it becomes red and deposits brown flakes of hydrated manganese dioxide : the red liquor is a solution of potassium permanganate, this salt being formed at the expense of the manganate, which breaks up into hydrated dioxide, potassium hydrate, and permanganate. 3K*MnO* -f 3H 2 = K 2 Mn 2 8 -f Mn0 2 .H 2 O + 4KOH Potassium Potassium Hydrated manganese manganate. permanganate. dioxide. An analogous decomposition takes place when an acid is added to the green solution of manganate; a manganous salt and permanganic acid are formed, and the latter colors the liquid red. 344 ELEMENTS OP MODERN CHEMISTRY. PERMANGANIC ACID. Potassium permanganate, K 2 Mn 2 8 , is an important salt. It may be prepared by introducing into an iron crucible 5 parts of caustic potassa with a small quantity of water, then a mix- ture of 3? parts of potassium chlorate and 4 parts of finely- powdered manganese dioxide. The mixture is heated and continually stirred, until the mass becomes dry and the tem- perature has reached dull redness. After cooling, the product is pulverized and introduced into 200 parts of boiling water. When the liquid has assumed a purple color, it is allowed to stand, decanted, and after neutralization by nitric acid, is evaporated at a gentle heat. On cooling, it deposits crystals that may be dried on a porous tile. Potassium permanganate crystallizes in almost black needles, having a metallic reflection. It dissolves in 15 or 16 parts of cold water, and its solution has a magnificent, intense purple color. If solution of sulphurous acid be added to potassium per- manganate solution, the latter is instantly decolorized, and the liquid contains only potassium sulphate and manganese sulphate. If a drop of the solution of potassium permanganate be placed upon a sheet of paper, it loses its color and a brown stain of hydrated manganese dioxide is produced. These experiments indicate the oxidizing properties of the permanganate. In the first, sulphurous acid was oxidized ; in the second, it was paper, of which the carbon and hydrogen removed the oxygen from the permanganate, which was thus reduced to dioxide. MANGANOUS SULPHATE. MnSCM + 7H 2 This salt may be prepared by dissolving manganous carbon- ate in sulphuric acid. The properly concentrated rose-colored solution deposits, between and 6, oblique rhombic prisms, isomorphous with green vitriol and containing 7 molecules of water. Between 7 and 20, manganous sulphate crystallizes with 5 MANGANOUS CARBONATE. 345 molecules of water, like cupric sulphate, with which it is then isomorphous. Between 20 and 30, it is deposited in oblique rhombic prisms, according to Marignac, which contain only 4 molecules of water. All of these crystals are rose-colored, and their color is deeper as they contain more water of crystallization. They are very soluble in water. MANGANOUS CARBONATE. The residues from the preparation of chlorine may be used for making this salt. They are evaporated, without filtering, in a porcelain capsule, with frequent stirring, and the dry residue is calcined with an excess of manganese dioxide. The ferric chloride which was mixed with the manganous chloride is decomposed or volatilized during this operation. Ferric oxide remains, mixed with the excess of manganese dioxide and the manganous chloride, which resists the heat. The latter is extracted by exhausting the mass with boiling water. A rose-colored solution is thus obtained which often contains a small quantity of cobalt chloride. The latter is precipitated as sulphide by adding little by little a solution of sodium sul- phide. As soon as the precipitate, which is at first blackish, begins to assume a flesh tint, the liquid is filtered and precipi- tated by sodium carbonate. Manganese carbonate constitutes a white powder with a pale rose tint. When heated in contact with air, it gives up car- bonic acid gas and is converted into red oxide of manganese. Characters of Manganese Salts. The salts of manganese are colorless or have a light rose color. Their solutions are not precipitated by hydrogen sulphide. Ammonium sulphide gives a flesh-colored precipitate ; sodium carbonate, a dirty white. Potassium hydrate produces a dirty white precipitate of manganous hydrate, which rapidly becomes brown by ab- sorbing oxygen from the air. When heated in the blow-pipe flame with a small quantity of potassium hydrate or nitrate, the salts of manganese give a bead which dissolves in water with a green color (manganate). p* 346 ELEMENTS OF MODERN CHEMISTRY. CHROMIUM. Cr = 52.5 Chromium was discovered in 1797, by Vauquelin, in a min- eral formerly known as red lead of Siberia, and which is chromate of lead. It forms one of the elements of chrome iron, a combination of chromium oxide with ferrous oxide, Cr 2 O 3 .FeO, which corresponds to magnetic oxide of iron, Fe 2 O 3 .FeO. H. Deville isolated the metal by calcining chromium oxide with charcoal and linseed oil in crucibles of lime and charcoal. Thus prepared, chromium forms grayish- white, metallic grains, which are brittle, as hard as corundum, and have a density of 5.9. This metal does not oxidize in the air at ordinary tempera- tures. At a red heat, it is converted into the oxide (VO 3 . When thrown into potassium chlorate in a state of fusion, it burns with a dazzling white flame, a chromate being formed. It burns in the same manner in chlorine gas, being transformed into a violet chloride. It dissolves in hydrochloric acid, disen- gaging hydrogen. COMPOUNDS OF CHROMIUM AND OXYGEN. There are two well-defined compounds of chromium and oxygen, the green oxide of chromium, Cr 2 3 , and chromic anhydride, CrO 3 . Chromium Oxide, Cr 2 O 3 , is a green powder; it may be obtained by calcining mercurous chromate. 2Hg 2 Cr0 4 = 4Hg -f O 5 + Cr 2 3 Another process consists in heating in a crucible a mixture of 2 parts of potassium dichromate with a little more than 1 part of flowers of sulphur. After cooling, the mass is treated with water, which dissolves out potassium sulphate and leaves chromium oxide. Fremy obtained it in small crystals by passing chlorine gas over potassium chromate heated to redness, and exhausting the cooled mass with water. Chromium oxide is undecomposable by heat, and melts only at the temperature of the forge. It forms several different CHROMIC ANHYDRIDE CHROMATES. 347 hydrates. When ammonia is added to the green solution of chromic chloride, a green, flaky precipitate of chromic hydrate is formed; it is soluble in acids and in potassium hydrate. Chromic Anhydride, CrO 3 , is prepared by gradually adding to a cold saturated solution of potassium dichromate 1? times its volume of sulphuric acid. The chromic anhydride, ordina- rily called chromic acid, set free separates in needle-shaped crystals of a dark-red color, which should be drained and re- crystallized in a small quantity of warm water. It is deliquescent; its aqueous solution has a dark yellow- brown color. It is an energetic oxidizing agent. Hydrochlo- ric acid converts it into chromic chloride, with evolution of chlorine. 2O0 3 -f- 12HC1 = O 2 C1 6 + 6H 2 + 3C1 2 If a concentrated solution of sulphurous acid be added to a solution of chromic acid, the liquid immediately becomes green from the formation of chromic sulphate. Chromates. The most important chromates are those of potassium and lead. Potassium neutral chromate, K 2 CrO*, crystallizes in lemon- yellow, right rhombic prisms, isomorphous with potassium sul- phate. It is very soluble in water, to which it communicates an intense yellow color. So great is its coloring property, that one part of chromate will sensibly color 40,000 parts of water. Potassium dichromate, K 2 Cr 2 7 , is prepared by heating to redness 2 parts of chrome iron with 1 part of nitre. The mass is exhausted with water, which dissolves out potassium neutral chromate; acetic acid is added to this solution, precipitating the silica, which is derived from the crucible and remains in the solution as silicate, and removing one-half of the potassium from the chromate, thus converting it into the dichromate. The latter crystallizes out on evaporation. Potassium dichromate is a beautiful salt of an orange-red color. It crystallizes in quadrangular tables derived from a dissymetric prism. It dissolves in 8 or 10 parts of cold water and in a much less quantity of boiling water. A strong heat decomposes it into neutral chromate, chromium oxide and oxygen. 2K 2 Cr 2 7 = 2K 2 O0 4 + Cr 2 3 -f O 3 348 ELEMENTS OP MODERN CHEMISTRY. When heated with sulphuric acid, it loses oxygen and is converted into chromic sulphate and potassium sulphate. K 2 GV0 7 + 4H 2 S0 4 = Cr 2 (S0 4 ) 3 + K 2 SO + 4H 2 + O 3 The residue when exhausted with water yields a green solu- tion, which deposits on evaporation beautiful octahedral crystals of a violet-black color, constituting chrome alum. Cr 2 (S0 4 ) 3 .K 2 S0 4 + 24H 2 Sulphurous acid reduces potassium dichromate in the cold, also yielding chrome alum if sulphuric acid be added. K 2 Cr 2 7 -f 3S0 2 + IFSO 4 = O 2 (S0 4 ) 3 .K 2 SO 4 -f H 2 The constitution of potassium dichromate is represented by the formula KOCrO 2 KOCrO 2 COMPOUNDS OF CHROMIUM AND CHLORINE. Several combinations of chromium and chlorine are known. The most important is the violet chloride, Cr 2 Cl 6 , correspond- ing to aluminium chloride and ferric chloride. It is prepared by passing chlorine gas over an intimate and perfectly dry mixture of chromium oxide and charcoal, heated to redness in a porcelain tube ; carbon monoxide is disengaged, and chromic chloride sublimes into the cooler portion of the tube in brilliant peach-blossom-colored scales. These crystals are almost insoluble in cold water, and dis- solve but slowly in boiling water. Hydrogen reduces them at a red heat, with formation of hydrochloric acid, and a chloride, Cr 2 Cl 4 , which crystallizes in white scales (Peligot). Cr 2 Cl 6 + H 2 = 2HC1 -f Ci*Cl 4 If a small quantity of the chloride Cr 2 Cl 4 , be added to hot water, holding in suspension the violet chloride, Cr 2 Cl 6 , the latter will be instantly dissolved, forming a green solution. Chlorochromic anhydride, Cr0 2 Cl 2 , is obtained by heating a previously fused mixture of common salt and potassium di- chromate with sulphuric acid ; abundant red vapors are disen- BISMUTH. 349 gaged, and condense to a blood-red liquid. This body boils at 116.8. Its density at 25 is 1.920 (Thorpe). On contact with water it decomposes into hydrochloric acid and chromic anhydride. O0 2 C1 2 + IPO = CrO 3 -f 2HC1 BISMUTH. Bi = 210 Extraction. This metal is found native in a quartzy gangue. It is extracted by simply heating the mineral in cast or sheet iron tubes, which are arranged in an inclined position in a fur- nace. The bismuth melts and runs out at an opening in the lower end of the tubes. The bismuth of commerce is never pure ; it contains traces of other metals, nearly always of arsenic and sometimes of sulphur. It is purified by pulverizing it, mixing it with -^ its weight of potassium nitrate, and heating the mixture to redness in a clay crucible. The foreign metals more oxidiza- ble than the bismuth are thus converted into oxides, the ar- senic into arsenate of potassium, and the sulphur into potassium sulphate. This treatment may be repeated a second time if necessary. Properties. Bismuth is a whitish-gray metal, having a yel- low lustre. Its fracture is crystalline and laminated. Its den- sity is 9.83, and it melts at 264. On cooling, it crystallizes in rhombohedra, of which the surfaces become covered with a thin film of oxide, causing a beautiful iridescent play of colors like that on a soap-bubble. Bismuth increases in volume on solidifying. It volatilizes at a white heat. It is unaltered by the air at ordinary tempera- tures, but at a red heat it absorbs oxygen and burns, forming bismuth oxide. Its best solvent is nitric acid, which converts it into nitrate. The various compounds of bismuth present great analogy to those of antimony, next to which this metal might be placed in the group including nitrogen, phosphorus, arsenic, antimony, and bismuth. 30 350 ELEMENTS OF MODERN CHEMISTRY. This analogy is shown in the following synoptic table : Bid 3 SbCP Bismuth trichloride. Antimony trichloride. Bi 2 3 Sb 2 3 Bismuth trioxide. Antimony trioxide. Bi 2 5 Sb 2 5 Bismuthic anhydride. Antimouic anhydride. Bi 2 0* Sb 2 4 Bismuth bismuthate. Antimony antimonate. Bi 2 S 3 Sb 2 S 3 Bismuth trisulphide. Antimony trisulphide. Otherwise, bismuth is related to the metals proper, not only by its properties, but by the facility with which it forms defi- nite salts. It is triatomic in its more important combinations, the oxide, chloride, and nitrate. BISMUTH TRIOXIDE. Bi 2 O 3 This body is obtained by decomposing the nitrate by heat. It is a straw-yellow powder, fusible at a red heat, and yielding on cooling a dark-yellow, vitreous mass. It attacks clay cruci- bles even more rapidly than litharge. A hydrated oxide of bismuth is formed when the nitrate or subnitrate is treated with potassium hydrate or ammonia. It is a white powder, insoluble in an excess of alkali, and when boiled with potassa, is converted into the crystalline anhydrous oxide. BISMUTH TRICHLORIDE. BiCl 3 Finely-divided bismuth will burn in chlorine, being con- verted into chloride. The latter is prepared by directing a current of chlorine upon melted bismuth contained in a retort. The chloride distils and solidifies in the receiver to a fusible, crystalline, and deliquescent mass, formerly known as butter of bismuth. A crystallized, hydrated chloride of bismuth may also be obtained by evaporating a solution of bismuth in nitro- hydrochloric acid. Bismuth chloride dissolves in water charged with hydro- chloric acid, but is decomposed when treated with pure water ; BISMUTH NITRATE. 351 in the latter case an oxychloride is formed and precipitated as a fine, white powder, hydrochloric acid being at the same time formed. 2BiCP + 2H 2 = 2BiOCl + 4HC1 Bismuth oxychloride is known as pearl-white. It contains BiOCl. BISMUTH NITRATE. Bi(NO 3 ) 3 Bismuth dissolves readily in nitric acid, and the concentrated solution deposits large, four-sided prisms, which are colorless and deliquescent. They contain Bi(N0 3 ) 3 -f 3H*0. They are very soluble in water acidulated with nitric acid, but if this solution be poured into a large excess of water, a pulverulent, white precipitate is formed, and increases in volume if very dilute ammonia be gradually added to the liquid in order to partly neutralize the free acid. This precipitate is much employed in medicine under the name of subnitrate of bismuth. Its composition is generally expressed by the formula BiNO* -f H 2 O = (BiO/NO 3 -j- H 2 O. It may be regarded as bismuthyl nitrate, that is, nitric acid, HNO 3 , in which the monobasic atom of hydrogen is re- placed by the monatomic group BiO. Or it may be considered as a derivative of orthonitric acid, H 3 N0 4 , corresponding to orthophosphoric acid, H 3 PO 4 (page 191). Boiling water removes still more nitric acid from this sub- nitrate, leaving a residue, which is used as a cosmetic, known as blanc de fard. Characters of Solutions of Bismuth. When mixed with X large quantity of water, bismuth solutions give white pre- cipitates of sub-salts. Hydrogen sulphide, and the soluble sulphides form a brown precipitate of bismuth sulphide, insolu- ble in an excess of ammonium sulphide. The alkaline hydrates and carbonates give white precipitates, insoluble in an excess of the reagent. Bismuth solutions are not precipitated by either sulphuric or hydrochloric acid. When heated with sodium carbonate in the reducing flame of the blow-pipe, compounds of bismuth yield a metallic globule, very brittle after cooling. 352 ELEMENTS OF MODERN CHEMISTRY. TIN. Sn (Stannum)= 118 Natural State and Extraction. The only mineral of tin which is worked is the dioxide (cassiterite). It is found in veins in the oldest formations, or disseminated in sand produced by their disaggregation. The principal tin mines are in India, in Malacca and the island of Banca, in Wales and in Saxony. Tin ore generally occurs mixed with various other minerals, such as sulphide and sulph-arsenide of iron, sulphides of copper and tin, etc. It is crushed and washed in order to remove light, earthy matters, and then roasted. The sulphides and sulph-arsenides are thus oxidized and disintegrated, and the product is submitted to a sec- ond washing which removes the lighter oxides, leaving the cassiterite. The latter is then heated with charcoal in a cupola-furnace, represented in Fig. 108; it is a sort of pris- matic furnace, having a hearth at the bottom where the melted metal collects. Air is blown in through the tuyere D. Car- bon monoxide is formed, and this reduces the stannic oxide ; the tin collects on the hearth, from which it is drawn into the basin I, where it is stirred with rods of green wood. The steam and gases produced by FIG. 108. the carbonization of the wood, agitate the melted mass and bring to the surface the foreign matter or dross, which is removed. The tin is then run into moulds. Thus obtained, tin generally contains small quantities of copper, iron, lead, antimony, and arsenic. It is purified by slowly heating it on the hearth of a reverberatory furnace; the pure tin melts first and runs out of the furnace, while the less fusible alloys remain upon the hearth. This method of purification is called liquation. Properties. Pure tin is a white metal, resembling silver in TIN. 353 its color and lustre. It melts at 228, and crystallizes when slowly cooled. Crystals of tin, belonging to the type of the right square prism, may also be obtained by galvanic precipi- tation of the metal. Their density is 7.178. That of the fused and slowly-cooled metal is 7.373 (H. Deville). Tin is ductile and malleable. When a bar of tin is bent, it produces a peculiar noise called the cry of tin. The metal is unaltered by the air, but when fused, rapidly becomes covered with a grayish pellicle of oxide. Tin dis- solves in concentrated hydrochloric acid, disengaging hydrogen. The action is rapid when heat is applied. If ordinary nitric acid be poured upon granulated tin, an energetic action takes place immediately. The tin is converted into a white powder of dioxide, and torrents of red vapors are evolved. Very dilute nitric acid attacks tin almost without disengage- ment of gas. After some time the liquid will be found to con- tain a small quantity of tin nitrate and ammonium nitrate. The ammonia is formed by the simultaneous reduction of water and nitric acid by the tin. HNO 3 + H 2 = 20 2 + NH 3 When tin is heated with a concentrated solution of either potassium or sodium hydrate, hydrogen is disengaged, and an alkaline stannate is formed. Uses of Tin. Tin enters into the composition of bronzes; it is made into dishes and covers, and the thin foil in which various substances, such as chocolate and tobacco, are enveloped. Tinning of kitchen vessels consists in covering them with a thin coating of tin. This protects the copper or iron from the action of the acids which enter into the composition of various articles of food. The objects to be tinned are first well cleaned by rubbing them with sand, and are then dipped into melted tin. After separating the excess of metal, they are polished by rubbing with cloths dipped in sal ammoniac. Tin-plate is sheet-iron covered with a thin layer of tin. The iron is first dipped into dilute sulphuric acid to remove the oxide; it is then rubbed with sand, and afterwards plunged successively into a bath of melted tallow and a bath of tin covered with tallow. On contact with the iron, the tin enters into com- bination, forming a true alloy, which becomes covered with a coating of pure tin. 30* 354 ELEMENTS OP MODERN CHEMISTRY. When the surface of tin-plate is washed with a mixture of hydrochloric and nitric acids, the superficial coat of tin is dis- solved, and the crystallized alloy of tin and iron is exposed. This is called crystallized tin-plate. COMPOUNDS OF TIN AND OXYGEN. Tin forms two compounds with oxygen, stannous oxide, SnO, and stannic oxide, SnO 2 . The first is of but little importance. It is obtained by precipitating a solution of stannous chloride by potassium hydrate, and boiling the precipitate, by which the white, stannous hydrate first formed is converted into a black crystalline powder of stannous oxide. When this substance is heated to 250, it decrepitates, increases in volume, and becomes converted into an olive-brown powder, which is a dimorphous modification of the black oxide. STANNIC OXIDE. SnO 2 This body is found in nature in the form of beautiful, hard, transparent crystals of a yellowish-brown color, belonging to the type of the square prism. The white powder obtained when the metal is treated with nitric acid is a stannic hydrate, which plays the part of an acid, and was named by Fremy metastannic acid. He attributes to it the composition 5(H*SnO*). It would be a polymere of normal stannic acid. When heated to 100, this hydrate loses half of its water; at a red heat, it loses the remainder and is converted into stannic oxide. When ammonia is added to an aqueous solution of stannic chloride, a white, gelatinous precipitate is formed, constituting a hydrate. This is the stannic acid of Fremy. It dissolves readily in hydrochloric acid, and the solution behaves as would an aqueous solution of stannic chloride. H 2 Sn0 3 + 4HC1 = SnCl* + 3H 2 SULPHIDES OF TIN STANNOUS CHLORIDE. 355 It reacts with the bases, forming stannates of which the general composition is expressed by the formula: R 2 Sn0 3 = I* 1 O 3 When heated to 140, or even when dried for a long time in a vacuum, it becomes insoluble in acids. SULPHIDES OF TIN. Two sulphides of tin are known : a monosulphide, SnS, and a disulphide, SnS 2 . The first is obtained by heating tin-filings with flowers of sulphur : the product still contains an excess of tin, and it is necessary to again heat it with a fresh quantity of sulphur. It is a crystalline, lead-colored mass. Tin disulphide or stannic sulphide is prepared by first making an amalgam of 12 parts of tin and 6 parts of mercury ; this is pulverized and the powder is mixed with 7 parts of flowers of sulphur and 6 parts of sal-ammoniac. The mixture is intro- duced into a matrass of green glass and gradually heated to dull redness on a sand-bath. Sulphur, sal-ammoniac, sulphide of mercury, and stannous sulphide are condensed in the upper part of the matrass, of which the interior becomes covered with a yellow crystalline mass of stannic sulphide. The presence of sal-ammoniac and mercury, which volatilize in this opera- tion, prevents an elevation of temperature, which would decom- pose the stannic sulphide. The latter is carried with their vapors, and condenses in brilliant, gold-like scales, which are greasy to the touch. This body is known as mosaic gold. It is decomposed by a red heat into stannous sulphide and sul- phur. It is used for coating the cushions of electric machines. STANNOUS CHLORIDE. SnCl 2 This compound may be prepared anhydrous by heating tin in hydrochloric acid gas. Hydrogen is evolved, and a white or grayish mass remains, which has a greasy appearance, and is almost transparent. It fuses at 250. This is stannous chloride. When tin is dissolved in hot, concentrated hydrochloric acid and the limpid solution is evaporated and allowed to cool, beautiful transparent crystals are obtained, which contain 356 ELEMENTS OF MODERN CHEMISTRY. SnCl 2 -f- 2H 2 0. This is known in commerce as tin salt or tin crystals. The crystals of stannous chloride dissolve in a small quan- tity of water, forming a limpid liquid, but when treated with a large quantity of water, they yield a cloudy liquid, which holds in suspension a small quantity of white oxy chloride. The atmospheric oxygen dissolved in the water takes part in this decomposition of stannous chloride, from which it removes part of the metal, a corresponding quantity of stannic chloride (tetrachloride) being formed. Stannous chloride reduces many oxygenized and chlorinated compounds. It decomposes the salts of silver and mercury, setting free the metal. It instantly decolorizes the purple solution of potassium permanganate. If a solution of stannous chloride be added to a solution of corrosive sublimate (mercuric chloride), a white precipitate of calomel (mercurous chloride) is instantly formed. By adding an excess of stannous chloride, all of the chlorine may be re- moved from the mercuric chloride, and a gray precipitate of metallic mercury will be formed. Stannous chloride is employed as a mordant in dyeing. STANNIC CHLORIDE (TETRACHLORIDE OF TIN). SnCl* If thin tin-foil be thrown into a jar of chlorine gas, the metal will take fire, and in presence of an excess of chlorine will be converted into anhydrous stannic chloride. This is liquid, and gives off white fumes in the air. It was formerly known as fuming liquor of Libavius. It is prepared by passing dry chlorine upon tin contained in a small retort. The anhydrous chloride condenses in the re- cipient in the form of a yellow liquid. It may be decolorized by rectification with a small quantity of mercury, which removes the excess of chlorine. Tin tetrachloride boils at 120. Its density is 2.28. A small quantity of water added to it is absorbed with a hissing noise, and the formation of a crystalline deposit of a hydrate, SnCl* + 5H 2 O. These crystals may also be obtained by dissolving tin in aqua regia and evaporating the solution, or, again, by passing chlo- LEAD. 357 rine into a solution of stannous chloride and concentrating the solution. The crystals of hydrated stannic chloride dissolve in water, forming a clear solution. Characters of Stannous Solutions. Brown precipitates are formed by both hydrogen sulphide and ammonium sulphide ; the precipitate dissolves in an excess of the latter reagent. Potassium hydrate forms a white precipitate, soluble in an excess of potassa ; ammonia yields a white precipitate, insoluble in excess. An excess of stannous chloride produces a gray precipitate of metallic mercury in a solution of mercuric chloride. Chloride of gold gives a purple precipitate (purple of Cas- sius) in dilute stannous solutions. Characters of Stannic Solutions. Hydrogen sulphide and ammonium sulphide form yellow precipitates, soluble in a large excess of the latter reagent. Potassa, soda, and ammonia, all form white precipitates, disappearing in an excess of the reagent. Chloride of gold does not precipitate stannic solutions. A sheet of iron or zinc will precipitate the tin from either stannous or stannic solutions in gray scales, which assume the metallic lustre when burnished. LEAD. Pb(Plumbum) = 207 Treatment of Lead Ores. The minerals of lead which are worked are the carbonate, and especially the sulphide, known as galena. The extraction of the metal from the carbonate is simple : it is heated with charcoal in a cupola-furnace, and the reduced lead collects on the hearth. Two methods are employed for the reduction of galena. One consists in melting the ore with iron (granulated cast iron). Sulphide of iron is formed, and both it and the reduced lead enter into fusion and separate from each other by virtue of their different densities, the lead being much the heavier. This is the reduction method. It is employed for impure ores having a silicious gangue. By the other process, known as the reaction method, the 358 ELEMENTS OP MODERN CHEMISTRY. galena is first roasted, by which the sulphide is partially trans- formed into oxide and sulphate ; the openings of the furnace are now closed and the temperature is elevated. The excess of sulphide then reacts upon the oxide and upon the sulphate ; sulphurous acid gas is disengaged, and metallic lead is formed. This is called work-lead. PbS + 2PbO = 3Pb -f SO 2 PbS + PbSO 4 == 2Pb -f- 2S0 2 The operation is conducted in a reverberatory furnace repre- sented in Fig. 109. The ore is spread in thin layers on the 3SWSSSS3W PIG. 109. hearth E, and heated to dull redness ; the fire is at A, and the air enters by the openings D. These are closed when it is judged by the aspect of the mass that the roasting is suffi- ciently advanced. The heat is then increased. Independently of the portion of lead sulphide which reacts upon the oxide and sulphate, there is always an excess, which melts when the heat is increased, and separates in the form of lead matt. This is subjected to another operation by the same process of reaction, and furnishes a harder lead than that first obtained ; it contains a small quantity of copper, and is known as slag lead. In some works, charcoal-powder is added at a certain stage of the roasting, to remove the oxygen from the oxide and sul- phate formed. LEAD. 359 Treatment of Argentiferous Lead. The lead produced by these methods, and especially the work-lead, often contains a small proportion of silver. In order to separate the latter metal, the lead is submitted directly to cupellation, or is first refined by way of crystallization before the cupellation. The object of refining by crystallization is the formation of an alloy of lead and silver, richer in silver than the work-lead. The argentiferous lead is melted and allowed to cool slowly; nearly pure lead separates in the form of crystals, which are deposited at the bottom of the molten metal. These -are re- moved by a ladle as fast as they are formed ; the richer alloy FIG. 110. of lead and silver remains liquid. The crystals of lead still contain a little silver, and are submitted to another fusion ; lead again crystallizes out on cooling, and a small quantity of an alloy still rich in silver is obtained. The same operation re- peated a third time determines the separation of pure lead. The alloys of lead and silver thus obtained are themselves sub- mitted to several successive fusions and crystallizations, and a still richer alloy results. The alloy thus concentrated is cupelled. The operation con- sists in melting the lead in a reverberatory furnace (Fig. 110), 360 ELEMENTS OF MODERN CHEMISTRY. of which the hearth has a hemispherical form, and is called the cupel. The vault of the furnace is formed by a sheet-iron cover, G, which can be raised and lowered at will. When the lead is melted, a strong blast of air is blown upon its surface through the tuyeres ft; the lead is thus converted into oxide, which melts and, driven by the current of air, flows from the cupel through a notch cut in its edge down to the level of the molten metal, and which is gradually deepened as that level becomes lowered. The silver, which is not oxidizable, becomes concentrated in the cupel as the lead is eliminated ; and when the last portions of the latter metal become oxidized, the sur- face of the silver is covered with only a thin layer of fused litharge, which breaks up suddenly and displays the brilliant surface of the metal. This phenomenon, called brightening, indicates the termination of the operation. The oxide of lead formed first in the cupellation of work- lead is called abstrich. It is black, and still contains a little silver, as well as copper and antimony (Berthier). The oxide which flows out after the abstrich is litharge. Properties of Lead. Lead is a bluish-white metal, having a certain degree of lustre when its surface is freshly cut. It is the softest and least tenacious of all the common metals. It can easily be cut with a knife and scratched by the finger-nail. It may readily be reduced to thin sheets, but is not easily drawn into wire. Its density is 11.363 (H. Deville). It melts be- tween 326 and 334, and volatilizes at a white heat. It may sometimes be obtained crystallized in regular octahedra by allowing a large quantity of molten lead to cool slowly, and decanting the still liquid portion. The brilliant surface of lead tarnishes in the air. When melted, it rapidly absorbs oxygen and becomes covered with a pellicle of oxide, which is transformed by the prolonged action of heat into a yellow powder, known as massicot. On contact with aerated water, lead absorbs oxygen and car- bon dioxide, and becomes covered with a thin layer of carbon- ate. This fact explains the presence of traces of lead in rain- water which has been collected from lead gutters, or kept in leaden reservoirs. The presence of small quantities of sulphates and chlorides in water prevents this oxidation of lead, so that the metal can be used without danger for the distribution of most spring and river waters. LEAD MONOXIDE. 361 Lead is rapidly dissolved by concentrated and boiling hydro- chloric acid. Dilute sulphuric acid does not attack it; the boiling concentrated acid converts it into sulphate with evolu- tion of sulphurous acid gas. Nitric acid attacks and dissolves it at ordinary temperatures, disengaging red vapors and forming lead nitrate. Lead and its compounds are poisonous. Its effects on the economy are especially manifested after the long-continued absorption of very small quantities of the metal, of which the accumulation in the system is made evident by various symp- toms; the best known is lead colic or painter 's colic. Plumbers, glaziers of pottery, painters, color-grinders, and the workmen employed in the manufacture of minium, or red lead, white lead, etc., are exposed to this chronic poisoning. The soluble sulphates are antidotes for acute cases of poisoning, and potas- sium iodide causes the elimination of lead from the system in chronic cases. Uses of Lead. This metal is used for the manufacture of shot, and pipes for the distribution of water and gas. When reduced to sheets it is made into gutters, the coverings of roofs, linings for troughs and reservoirs. Sheet-iron dipped into a bath of melted lead retains a coating of that metal, and is called leaded iron. Lead enters into the composition of type-metal, plumber's solder, pewter, etc. LEAD MONOXIDE. PbO Massicot and litharge, of which the formation has been in- dicated, constitute the monoxide of lead. Massicot is a yellow, amorphous powder. Litharge occurs in reddish-yellow, crystalline scales. It is rendered crystalline by the fusion and cooling through which it passes. It is sometimes met with in the form of rhombic octahedra (Mitscherlich). Oxide of lead melts at a red heat ; when fused it absorbs oxygen, which it again gives up on solidifying (F. Le Blanc). It cannot be melted in an earthen crucible without attacking and sometimes piercing the latter, owing to the formation of a very fusible silicate of lead. Lead monoxide is easily reduced by hydrogen, charcoal, and carbon monoxide. It is very slightly soluble in water, and possesses a sufficiently Q 31 362 ELEMENTS OF MODERN CHEMISTRY. marked alkaline reaction to restore the blue color to feebly reddened litmus-paper. When potassium hydrate or ammonia is added to a solution of a salt of lead, a white precipitate, which is a hydrate of lead, is formed. This hydrate dissolves in an excess of potassium hydrate ; it is also soluble in lime-water, and these solutions are precipitated black by hydrogen sulphide. Litharge is used for the manufacture of lead acetate and white lead. It gives to linseed oil drying properties. It enters into the composition of various plasters, and different coloring matters (Cassel's yellow). LEAD DIOXIDE. PbO 2 This body is made by treating minium, or intermediate oxide of lead, with dilute nitric acid. A brown powder remains and must be washed with boiling water. This is dioxide of lead ; it is insoluble in water ; it is readily decomposed by heat, losing half of its oxygen and being converted into monoxide. It is an energetic oxidizing agent. When it is briskly triturated with a small quantity of sulphur, the latter is inflamed. If lead dioxide be introduced into a test-tube filled with sul- phurous acid gas, the latter is immediately absorbed with for- mation of lead sulphate. SO 2 + PbO 2 = PbSO 4 Hydrochloric acid poured upon lead dioxide determines the formation of lead chloride and the disengagement of chlorine. PbO 2 + 4HC1 == PbCl 2 + Cl 2 + 2H 2 Lead dioxide unites with the alkalies forming veritable salts. Fremy has described a plumbate of potassium, K 2 Pb0 3 -f 3H 2 0, which crystallizes in cubes, and which is formed when dioxide of lead is gently heated with a very concentrated solu- tion of potassium hydrate in a silver crucible. PLUMBOSO-PLUMBIC OXIDE (RED LEAD) This oxide is prepared by heating massicot in furnaces to a temperature that should not exceed 300. Under these con- ditions, the monoxide absorbs oxygen from the air, and is con- LEAD SULPHIDE. 363 verted into a beautiful red powder known as minium or red lead. The product obtained by heating lead carbonate or white lead in contact with the air is called orange minium. Minium is a combination of monoxide and dioxide of lead ; its composition is variable, according to the length of time it is roasted. It ordinarily corresponds to the formula Pb 3 4 = 2PbO.Pb0 2 (Jacquelain) Sometimes it contains less oxygen, having the composition Pb 4 5 = 3PbO.Pb0 2 (Mulder) Red crystals of the latter composition have been found in the fissures of a minium furnace. Minium has a scarlet-red color, which becomes much darker on heating. It gives up oxygen at a red heat, being reduced to monoxide. If red lead be sprinkled with nitric acid, the color disappears, giving place to a brown. The nitric acid removes the monoxide, forming nitrate, and leaves the brown dioxide. Minium is used to color sealing-wax and wall-papers. It is employed in the manufacture of flint glass, which owes its fusi- bility, its perfect transparency and its refractive power, to sili- cate of lead. When mixed with stannic oxide, minium serves as an enamel for crockery-ware. A mixture of red lead and white lead with a small quantity of oil is employed as a luting for steam-pipes, and as a cement. LEAD SULPHIDE. PbS Galena or sulphide of lead occurs in nature in beautiful cubical crystals of a bluish-gray color and a metallic lustre ; its density is 7.58. It melts at a red heat. When heated in con- tact with air, it is converted into oxide and sulphate, and by the reaction of an excess of sulphide upon these compounds me- tallic lead is produced. Hot fuming nitric acid converts lead sulphide into sulphate. Concentrated and boiling hydrochloric acid transforms it into chloride with evolution of hydrogen sulphide. Galena is used for glazing common pottery. A broth of powdered galena and cow's dung mixed with water is applied to the surface of the previously well-dried vessels. 364 ELEMENTS OP MODERN CHEMISTRY. This sort of pottery is generally baked at a temperature not very high, so that the sulphide of lead, the oxidation of which is prevented by the cow's dung, melts and spreads over the sur- face, forming a varnish of a dark color when cold. Neverthe- less, a small quantity of oxide is always formed by the oxidation of the galena : when the baking takes place at a higher temper- ature, this oxide forms a fusible silicate, which covers the pottery. This glazing often has a green color, due to the presence of oxide of copper, and is attacked by vinegar and other acids, which dissolve the oxides of lead and copper. Hence the danger in the use of ware so glazed for culinary purposes. LEAD CHLORIDE. PbCP This body may be obtained as a white, crystalline powder by heating litharge with hydrochloric acid. It is deposited as a dense, white precipitate when hydrochloric acid is added to a concentrated solution of acetate or nitrate of lead. It is not very soluble in water; 135 parts of water at 12.5, or 33 parts of boiling water being required to dissolve one part of lead chloride. It may be obtained crystallized in long needles by allowing its saturated boiling solution to cool. Lead chloride melts below a red heat, and on cooling solidifies to a semi-trans- parent mass, known by the ancient chemists as horn-lead. Mineral yellow, Turner s yellow, and CasseTs yellow, em- ployed in painting, are oxychlorides of lead, combinations of lead oxide and chloride in variable proportions. LEAD IODIDE. PbP When a solution of potassium iodide is added to a solution of lead acetate, a beautiful yellow precipitate of lead iodide is formed. This body melts to a red-brown liquid at a high temperature. It requires for solution 1235 parts of cold, or 194 parts of boiling water. On the cooling of its saturated, boiling solution, it is deposited in golden-yellow, hexagonal scales having a mag- nificent lustre. LEAD NITRATE LEAD SULPHATE. 365 LEAD NITRATE. Pb(NO 3 ) 2 This body is prepared by dissolving litharge in dilute nitric acid. It crystallizes from its hot, saturated solution in anhy- drous, white, regular octahedra. These crystals decrepitate when they are heated ; they dissolve in 7 i times their weight of cold water, and in a much less quantity of boiling water. At a red heat this salt is decomposed into nitrogen peroxide, oxygen, and lead monoxide. It forms various basic compounds with lead monoxide. When one molecule of the nitrate is boiled with one molecule of the monoxide, and the filtered solution is allowed to cool, a crystalline deposit is obtained, which is a dibasic nitrate, Pb(N0 3 ) 2 H- Pb -f H 2 (Pelouze). This salt can be consid- ered as derived from orthonitric acid, H 3 NO* = HNO 3 -f- H 2 0. Indeed Pb(N0 3 ) 2 + PbO + H 2 = 2^ b 1 NO* This basic nitrate of lead corresponds to the basic nitrate of bismuth, (page 351). Bi"'NO* P g j NO 4 Bismuth subnitrate. Lead sulmitrate. When a solution of nitrate of lead is boiled with thin sheet- lead, the latter is dissolved, and the liquid assumes a yellow color. Under these conditions soluble basic nitrites of lead are formed. On cooling the filtered liquid deposits yellow crystals having a variable composition. By a prolonged boiling a tetra- basic nitrite, Pb(N0 2 ) 2 -f- 3PbO -f H 2 0, is obtained. The so- lution of the latter, decomposed by carbon dioxide, gives the neutral nitrite Pb(NO 2 ) 2 -j- H 2 0, crystallizing in long, yellow prisms (Peligot) or in yellow plates (Chevreul). LEAD SULPHATE. PbSO This salt is found crystallized in nature. It can be prepared by double decomposition by precipitating the solution of any soluble lead salt, such as the nitrate or acetate, with sulphuric acid or solution of a sulphate. It is a white powder, insoluble in water. 31* 366 ELEMENTS OF MODERN CHEMISTRY. At a high temperature, lead sulphate melts without decom- position. Charcoal reduces it, transforming it into sulphide, metal, or oxide, according to the proportions employed. Quickly heated with an excess of charcoal, it yields sulphide. PbSO* + C 2 = 2C0 2 + PbS By diminishing the proportion of charcoal, a residue of metal, or even of oxide, may be obtained. PbSO* -f C = CO 2 + SO 2 + Pb 2PbS0 4 -f- C = CO 2 -f 2S0 2 + 2PbO Iron and zinc, in contact with lead sulphate suspended in water, cause the separation of metallic lead. LEAD CARBONATE. PbCO 3 Crystallized lead carbonate is found in nature. The salt may be obtained artificially, as an amorphous white powder, by precipitating a soluble lead salt by an excess of an alkaline carbonate. A hydrated, and sometimes basic, carbonate of lead is known as ceruse or white lead. Its composition varies. PbCO 3 + H 2 and 2PbC0 3 + Pb(OH) 2 These are much used in oil painting. White lead is pre- pared by several methods, the oldest of which is called the Dutch process. It consists in exposing sheets of lead to an atmosphere charged with acetic acid vapor and rich in carbonic acid gas. The leaden sheets are introduced into glazed earthen pots, A (Fig. Ill), containing a small quantity of vinegar. The lead rests upon short projecting arms, B, below which is placed the crude vinegar. The pots are covered by a disk of lead, D, which incompletely closes them. FIG. 111. They are then arranged in rows in large chambers; a row of pots is placed on a bed of spent tan or horse-manure ; these are cov- ered with planks, upon which more spent tan or horse-manure is placed, and then another layer of pots, and so on. The fer- LEAD CHROMATE. 367 mentation of the tan or manure raises the temperature to 30 or 40, and produces carbonic acid gas. On the other hand, the oxygen of the air intervenes, causing the lead to be attacked by the acetic acid, so that basic acetate of lead is formed upon the surface of the metal ; but this salt is con- tinually decomposed by the carbonic acid gas, so that the lead gradually becomes covered with a layer of carbonate. Thenard suggested another process by which litharge is dis- solved in a solution of lead acetate, and a current of carbon dioxide passed through the solution of subacetate so formed. Lead carbonate is precipitated and neutral acetate regenerated ; the latter is then again transformed into basic acetate. The product so obtained is known as Clichy white lead. LEAD CHROMATE. PbCrO* This salt exists crystallized in nature, constituting the red lead of Siberia. It is prepared by double decomposition between solutions of potassium chromate and lead acetate ; a yellow precipitate is thus obtained, and is employed in painting under the name chrome yellow, Lead chromate melts at a red heat ; at a white heat it loses 4 per cent, of oxygen. It is easily reduced by charcoal and hydrogen. Insoluble in water, it dissolves readily in solutions of potassium hydrate. Characters of Lead Salts. The soluble lead salts have a sweetish taste. Black precipitates are formed in their solutions by both hydrogen sulphide and ammonium sulphide. Potassa and soda yield white precipitates, soluble in a large excess of the reagent. Ammonia gives a white precipitate, insoluble in excess. Sulphuric acid forms a white precipitate even in the most dilute solutions of lead. Hydrochloric acid forms a white precipitate of lead chloride, but this precipitate is not produced in dilute solutions. Potassium chromate throws down a yellow precipitate, soluble in potassium hydrate. When heated with sodium carbonate upon a piece of charcoal in the reducing flame of the blow-pipe, the lead salts yield a metallic globule which when cold can readily be flattened out by hammering. 368 ELEMENTS OP MODERN CHEMISTRY. COPPER Cu(Cuprum) = 63.5 Natural State. Copper is found in the native state, some- times crystallized in regular octahedra, sometimes in masses. It is also found as cuprous oxide, Cu 2 O, cupric oxide, CuO, and cupric carbonate, CuCO 3 ; but its most abundant minerals are cuprous sulphide, Cu 2 S (Chalkosine), and a double sulphide of copper and iron, Cu 2 S.Fe 2 S 3 , designated as copper pyrites. Under the name gray copper are also worked various minerals containing cuprous sulphide combined with the sulphides of antimony and arsenic, and in which the copper is sometimes replaced by iron, zinc, silver, and mercury. Treatment of Copper Ores. Copper is easily extracted from cuprous oxide and cupric carbonate. These ores are melted with charcoal in suitable furnaces, and the metal is at once obtained. Copper pyrites, which is often mixed with cuprous sulphide, requires a more complicated treatment. The iron and sulphur must be eliminated, and for this reason the ore is subjected to an incomplete roasting. This operation is conducted in a reverberatory furnace (Fig. 112). The flame FIG. 112. of the fire sweeps the arched vault of the furnace w. The opening of the chimney is at C, and the ore is fed in from iron troughs placed above the furnace. COPPER. 369 The first roasting drives out part of the sulphur, and the sulphides of iron and copper are partially converted into oxides and sulphates. An excess of sulphide remains, and the im- perfectly-roasted ore is fused in presence of silicious materials. The scoriae formed in roasting the matt (see farther on) are generally added, and sometimes fluor spar, to render the slag more fusible. This operation is conducted either in cupola-fur- naces or in reverberatory furnaces of peculiar construction. In presence of the unattacked sulphide of iron, the cupric oxide formed during the roasting is converted into cupric sulphide, and oxide of iron is formed. The latter unites with the silica, as does also the oxide produced by the roasting, both being reduced to ferrous oxide by the reducing gases of the fire. Ferrous sili- cate is thus formed, and constitutes a very fusible slag, below which accumulates the sulphide of copper containing much less sulphide of iron than the original pyrites. This product is the matt. The sulphur, which was thus far necessary to expel the iron, must now be removed, and the matt is broken up and repeat- edly roasted, by which the remainder of the iron is oxidized and nearly all of the sulphur expelled. The mineral is now again melted with silicious materials and the scoriae produced in re- fining black copper, and rich in cupric oxide, are added. Ferrous silicate separates as a slag, and a metallic mass containing from 90 to 94 per cent, of copper, still alloyed with iron, lead, arsenic, sulphur, etc., is obtained. This product constitutes black copper. Refining of Black Copper. The impure metal is melted in a reverberatory furnace ; the oxygen of the air transforms the copper into oxide, and the latter is gradually reduced by the foreign metals and the sulphur still contained in the mass of copper ; these oxides separate in the form of scoriae and slags, which are removed. The liquid copper collects in a cylin- drical cavity in the furnace, where it is solidified by throwing cold water upon the surface of the molten metal ; it is then removed in the form of disks, and is called rosette copper. The copper thus obtained is brittle, owing that property to the cupric oxide with which it is still impregnated. It is finally melted under a layer of charcoal, and stirred with poles of green wood. Red, ductile copper is thus obtained. At Mansfeld, in Prussia, a copper pyrites is worked which Q* 370 ELEMENTS OF MODERN CHEMISTRY. is disseminated in little crystals in an argillaceous schist impreg- nated with bitumen. After a series of roastings and smeltings, a black copper is obtained, rich enough in silver to permit of the advantageous extraction of that metal. For this purpose the method called liquation is employed. The argentiferous copper is melted with lead, and the liquid alloy is allowed to cool slowly. Copper solidifies first, alloyed with a small quan- tity of lead, while the remainder of the lead, retaining nearly all of the silver, remains liquid. By another process the alloy of lead and argentiferous copper is made into disks, D (Fig. 113), and these are reheated very slowly. As soon as the temperature is suf- ficiently high, the lead melts and runs out, carrying with it all of the silver. The copper remains al- loyed with a small quantity of lead. It is refined by melting it in a cu- pola-furnace under the blast of a FIG. 113. tuyere. The lead and iron and part of the copper are oxidized, and the oxides are removed as scoriae. Pure copper remains and is converted into rosette. The argentiferous lead is sub- mitted to cupellation, as already described. Cement copper is copper precipitated from a solution of cupric sulphate by metallic iron. It is very pure. Properties of Copper. This metal has a characteristic red color that is universally known. When rubbed with the hand it exhales a peculiar, disagreeable odor. By fusion it crystal- lizes in cubes, but it may be deposited by electrolysis in reg- ular octahedra. It melts towards 1100, and maybe volatilized by the heat of the oxy-hydrogen blow-pipe. Its density varies from 8.85 to 8.95. It is very malleable, ductile, and tenacious. In dry air it is unaltered at ordinary temperatures, but it absorbs oxygen in presence of moisture and carbonic acid gas. Green spots are then formed upon the surface of the metal, constituting a hydrocarbonate of copper ; this is the product ordinarily called verdigris. At a high temperature copper absorbs oxygen with avidity, being converted into black, cupric oxide if the oxygen be in excess ; but in the contrary case, red. cuprous oxide is formed. The oxidation is favored by division of the metal. CUPROUS OXIDE. 371 If some pulverulent copper, produced by the decomposition of copper acetate, be thrown upon a moderately hot tile and an incandescent coal be approached so as to heat one point, a black spot instantly forms there and rapidly extends throughout the mass, showing the progress of the oxidation. In presence of acids or ammonia, copper rapidly absorbs oxygen at ordinary temperatures. If some ammonia and copper-turnings be shaken up with air in a glass-stoppered bottle, the ammoniacal liquid becomes blue; if now the bottle be turned upside-down and opened under water, the latter will rise in the bottle, replacing the oxygen which was absorbed. The blue liquid contains in solution am- moniacal oxide of copper and nitrite of copper (Schonbein, Peligot). This liquid is capable of dissolving cotton and lint, which are almost pure cellulose (Schweizer). When heated with concentrated sulphuric acid, copper is converted into sulphate with disengagement of sulphurous acid gas. Nitric acid, even dilute, dissolves it readily, forming cupric nitrate and evolving nitrogen dioxide. Boiling hydro- chloric acid attacks it slowly, disengaging hydrogen and forming cuprous chloride. Uses of Copper. Copper is much employed for the con- struction of boilers, alembics, stills and worms, and for kitchen utensils. Sheet-copper is used for coating the bottoms of ships and sometimes for roofing houses. This metal enters into the composition of the more important alloys, brass (copper and zinc), bronze (copper and tin), German silver (copper, zinc, and nickel). CUPROUS OXIDE. Cu 2 O This oxide is found in nature, sometimes in vitreous masses, sometimes in beautiful, red, regular octahedra. It is ordinarily prepared in the wet way by boiling a solution of acetate of copper with glucose ; a bright-red, crystalline pow- der is precipitated, which is anhydrous cuprous oxide. When heated in contact with air, it absorbs oxygen and is converted into cupric oxide. When potassium hydrate is added to a solution of cuprous chloride, a yellow precipitate of cuprous hydrate is thrown down. Cuprous oxide is used to communicate a red color to glass. 372 ELEMENTS OP MODERN CHEMISTRY. CUPRIC OXIDE. CuO Two processes are used for the preparation of this important body : calcination of copper in the air ; calcination of cupric nitrate. The first method furnishes a granular, compact, black oxide ; the second, a fine, deep-black powder. Cupric oxide is easily reduced by both hydrogen and char- coal, with formation of either water or carbon dioxide. With water it forms a hydrate, Cu(OH) 2 as CuO.H 2 0, which precipitates as a thick, light-blue magma, when potassium hy- drate is added to a cupric solution. This hydrate is converted into brown, anhydrous oxide by boiling with water. Cupric oxide is largely used in the laboratory in the analysis of or- ganic substances. It is used in the arts to color glass, to which it imparts a green color. SULPHIDES OF COPPER. Copper forms two sulphides, corresponding to the oxides. Cuprous sulphide, Cu 2 S, occurs in nature in fusible, steel-gray crystals, which may be scratched with a knife. Cupric sulphide CuS, is formed in the wet way when a solution of a copper salt is precipitated by hydrogen sulphide. When strongly calcined, it loses sulphur and is reduced to cuprous sulphide. If copper filings or turnings be thrown into a flask containing boiling sulphur, a brilliant incandescence takes place from the union of the two elements. CHLORIDES OF COPPER. Cuprous chloride, Cu 2 Cl 2 , is prepared by boiling copper- turnings in hydrochloric acid and adding small quantities of nitric acid from time to time. The nitro-muriatic acid formed converts the copper into cupric chloride, which is reduced by the excess of copper present. A brown liquid is thus obtained which, by continued boiling, becomes almost colorless. On adding water to this liquid, a white, crystalline precipitate of cuprous chloride is deposited. It is insoluble in water, but dis- solves in aqueous ammonia, forming a liquid which remains colorless when kept in closed vessels in presence of an excess CUPRIC SULPHATE. 373 of copper, but becomes blue on exposure to the air, from which it absorbs oxygen. Carbon monoxide is perfectly absorbed by a solution of cuprous chloride in hydrochloric acid or in ammonia. Cupric chloride, CuCF, is obtained by dissolving cupric oxide in hydrochloric acid or in aqua regia. A green solution is formed, which, after concentration, deposits beautiful rhombic prisms of a bluish-green color, containing 2 molecules of water of crystallization. CUPRIC SULPHATE. CuSO* + 5H 2 O Preparation. This salt is commonly called blue vitriol. It is a product of many industrial operations, such as roasting sulphurous copper ores, and the decomposition by copper of the silver sulphate resulting from the refining of gold, that is, the treatment of silver coin containing gold with sulphuric acid. Cupric sulphate produced by roasting copper ore contains more or less ferrous sulphate. The two salts crystallize together in oblique rhombic prisms, containing 7 molecules of water of crystallization. The mixture is called Salzburg vitriol. Instead of copper pyrites, artificial cupric sulphide may be oxidized. Old copper plates are moistened and sprinkled with flowers of sulphur ; they are then heated in a furnace, and the sulphide of copper first formed is converted into sulphate by the oxygen of the air drawn into the furnace. The still hot plates are plunged into water, which dissolves the layer of cupric sulphate, and the same operation is repeated until all of the metal is transformed into sulphate. The simplest process consists in boiling copper turnings and clippings with sulphuric acid : sulphurous acid gas is disen- gaged, and cupric sulphate formed. In the arts, the operation is conducted in wooden tanks lined with lead and heated by steam. Properties. Cupric sulphate crystallizes in parallelopipedons belonging to the type of the dissymetric prism. These crystals have a fine blue color, and contain 5 molecules of water. When exposed to dry air they effloresce superficially : heated to 100, they lose 4 molecules of water, disengaging the fifth only at 243. The anhydrous salt is white. At a high heat, cupric 32 3*74 ELEMENTS OF MODERN CHEMISTRY. sulphate is decomposed into cupric oxide, sulphurous oxide, and oxygen. Cupric sulphate dissolves in 4 parts of cold, and in 2 parts of boiling water, and the concentrated solution has a pure blue color. It is insoluble in alcohol. When an excess of ammonia is added to a solution of cupric sulphate, a beautiful, dark-blue liquid is obtained. It contains ammoniacal cupric sulphate, CuSO 4 -j- 4NH 3 -f- IPO, which separates in dark-blue crystals when alcohol is added to the aqueous solution. There are several basic sulphates of copper representing compounds of cupric sulphate and cupric hydrate. One of them is obtained as a green powder when a solution of cupric sulphate is digested with cupric hydrate. The bluish precipi- tates obtained by incompletely precipitating solutions of cupric sulphate with potassium hydrate are basic sulphates. Uses. Cupric sulphate is employed as a caustic applicable to diseases of the eye. In the arts, it is used in the prepara- tion of blue ashes, a mixture of calcium sulphate and cupric hydrate, made by decomposing cupric sulphate with milk of lime. It is much used in dyeing, particularly in dyeing black on wool and cotton. Its solution is used for steeping wheat. Large quantities of sulphate of copper are employed for elec- trotyping. CARBONATES OF COPPER. When cold solutions of sodium carbonate and cupric sul- phate are mixed, a bluish-green precipitate is obtained, and at the same time carbonic acid gas is disengaged. The precipi- tate becomes green when washed with warm water. It is known as mineral green, and can be regarded as a combina- tion of one molecule of cupric carbonate with one molecule of cupric hydrate. It contains CuCO 3 + Cu(OH) 2 A similar compound exists in nature, constituting malachite. This mineral occurs in green masses. When cut and polished, it presents veins of various tints, and is fashioned into orna- mental objects, such as vases, cups, etc. Azurite or mountain blue, which crystallizes in beautiful, CARBONATES OF COPPER. 3*75 blue, oblique rhombic prisms, can be regarded as a compound of two molecules of cupric carbonate with one of the hydrate. 2CuC0 3 + Cu(OH) 2 Debray has reproduced azurite artificially by leaving calcium carbonate for a long time in contact with cupric nitrate in sealed tubes. ALLOYS OF COPPER. Brass is an alloy of copper and zinc, ordinarily containing ^ zinc and f copper. It often contains a small proportion of tin and even of lead. Bronze is an alloy of copper and tin (see table of alloys, page 237). While brass is malleable and ductile, bronze is brittle when it has been slowly cooled, but it becomes malleable after tempering, that is, when it is heated to redness and then plunged into cold water. German silver contains 25 per cent, of zinc, 25 of nickel, and 50 of copper. Characters of Copper Salts. These salts are blue or green. Their solutions are precipitated brown by hydrogen sulphide and ammonium sulphide ; an excess of the latter reagent will not dissolve the precipitate. Potassium hydrate forms a dense, light-blue precipitate, in- soluble in excess. Ammonia first forms a pale-blue precipitate, which is then dissolved by an excess of the reagent with a rich sky-blue color. Potassium ferrocyanide gives a chestnut-brown precipitate even in very dilute cupric solutions. An apple-green precipitate of cupric arsenite (Scheele's green) is formed when potassium arsenite is added to cupric sulphate. A bright piece of iron plunged into a cupric solution in- stantly becomes covered with a deposit of metallic copper. MERCURY. Hg (Hydrargyrum) = 200 Natural State and Extraction. Mercury occurs native, and especially combined with sulphur, mercuric sulphide or natural cinnabar being its principal ore. It is found in differ- 376 ELEMENTS OF MODERN CHEMISTRY. ent localities in Europe and America, principally at Almaden, Spain; Idria, in Illyria; San Jose, in California. The treatment of the ore is very simple. The sulphide is roasted in a current of air in furnaces of peculiar construction : the sulphur is oxidized, and passes off as sulphur dioxide, the mercury being set free. The metal volatilizes and is led, to- gether with the gases from the combustion, either into con- densation-chambers, or through long rows of little cylindrical vessels, where the mercury condenses. Fig. 114 represents the furnaces employed at Almaden, with the fireplace, and the body, AB, charged with ore. The FIG. 114. mercury-vapor passes by o, and condenses in a series of aludels entering one in the other, and arranged upon two inclined planes, ab, be. The condensed metal runs into a channel, 6, from which it is conducted into a reservoir. The sulphurous acid gas, still charged with vapor of mercury, passes into a chamber, C, descending to the floor, where it is cooled by contact with a trough filled with water, d. In this chamber the condensation of the mercury-vapor is completed. Fig. 115 represents the several-storied furnaces aa, &6, cc, and the condensation-chambers CC, used at Idria. Cinnabar may also be reduced by iron or by lime. The metal thus extracted is purified by filtration through ticking-cloth or chamois-skin. It is ordinarily transported in forged iron bottles. The mercury of commerce is nearly always alloyed with small quantities of other metals, such as lead, tin, copper, and bis- MERCURY. 377 muth. In this state its surface is not as brilliant as when pure, it does not run as readily, and the drops are drawn out to a point. They are said to form tails. It may be purified by dis- tillation, an operation which requires certain precautions, and which is ordinarily eifected in the iron bottles which serve for the transportation of the metal. It may also be purified by digesting it for several days with one-thirtieth its weight of commercial nitric acid diluted with its own weight of water ; the aqueous liquid is then decanted and the mercury washed, first with warm water acidulated with nitric acid, then with pure water, after which it can be dried. In this operation, the nitric acid removes the foreign metals, more oxidizable than the mercury, which displace the latter metal from its solution in the nitric acid. FIG. 115. Properties, Mercury is liquid, but solidifies at 40. The solid metal at this low temperature is malleable, and has a density of 14.4. The density of liquid mercury is 13.595. It boils at 350 of an air thermometer. Its vapor is colorless, and has a density of 6.976. It is unaltered by contact with the air at ordinary tempera- tures, but at 300 it slowly absorbs oxygen, and its surface becomes covered with a red powder, which is mercuric oxide, called by the ancients red precipitate. Mercury combines with chlorine, bromine, and iodine at ordi- nary temperatures, and with sulphur by the aid of a gentle heat. 378 ELEMENTS OP MODERN CHEMISTRY. Hydrochloric acid does not attack it. Dilute nitric acid dis- solves it in the cold, forming mercurous nitrate. Hot nitric acid dissolves it, forming mercuric nitrate and evolving red vapors. OXIDES OF MERCURY. Two oxides of mercury are known, mercurous oxide, Hg 2 0, and mercuric oxide, HgO. The first is prepared by digesting mercurous chloride (calo- mel) with potassium hydrate ; a black powder is obtained which is very unstable. By the action of light, or by a temperature above 100, it decomposes into mercuric oxide and mercury. Mercuric Oxide, HgO, can be obtained by either the dry or wet method. The first consists in decomposing mercuric nitrate by heat; the salt is gradually heated in a flask on a sand- bath until red vapors cease to be disengaged. The oxide thus prepared is an orange-red, granular, and crystalline powder. Mercuric oxide is prepared in the wet way by decomposing a solution of mercuric chloride by potassium hydrate. A yellow precipitate of anhydrous mercuric oxide is obtained. When mercuric oxide is heated, it assumes a dark-red color and decomposes, if the temperature be above 400, into oxygen and mercury. It yields its oxygen to many bodies, such as charcoal, sulphur, and phosphorus, which it oxidizes energet- ically. When heated with sulphur, it produces an explosion. In these reactions the finely-divided yellow oxide is more active than the red oxide. MERCURIC SULPHIDE. HgS This is the cinnabar generally fotfnd in nature in compact masses, sometimes in transparent, red, hexagonal prisms or rhombohedra. It is manufactured by directly combining sul- phur and mercury. The combination takes place when the bodies are triturated together in the cold, in the proportion of 100 parts of mercury and 18 parts of sulphur. A black mass is thus obtained which is sublimed in iron vessels. Cinnabar prepared by sublimation occurs in dark-red masses, having a fibrous and crystalline structure. Its density is 8.124. At a high temperature, it volatilizes without melting. When MERCUROUS CHLORIDE. 3*79 heated in the air, it burns with a blue flame, yielding sulphur- ous acid gas and metallic mercury. It is decomposed by hydro- gen, charcoal, and most of the metals. Boiling sulphuric acid decomposes it with formation of sulphurous acid gas and sul- phate of mercury. Nitric acid scarcely attacks it, even when boiling. Vermillion is a finely-divided mercuric sulphide having a rich scarlet color. It is prepared by triturating for several hours in a mortar, 300 parts of mercury and 114 parts of flowers of sulphur, and adding to the black sulphide thus ob- tained 75 parts of potassa and 400 parts of water. The mixture is maintained at a temperature of about 45, being continually triturated with a pestle. As soon as the powder has acquired a fine scarlet color, it is rapidly washed with hot water and dried. It is employed in painting and also to color sealing- wax. MERCUROUS CHLORIDE, OR CALOMEL. HgCl> Mercurous chloride is largely used in medicine under the name calomel or mild chloride of mercury. Preparation. An intimate mixture of mercurous sulphate and sodium chloride is heated in a capacious glass matrass on a sand-bath. The mercurous chloride, formed by double decom- position, sublimes. Hg 2 S0 4 +.2NaCl Hg 2 Cl 2 + Na'SO 4 It is thus obtained in compact, crystalline masses. When it is strongly heated and its vapor passed into large stoneware vessels filled with steam, it condenses in an impalpable powder, in which form it is used by preference in medicine. Calomel may also be prepared in the wet way by adding hydrochloric acid, or a solution of sodium chloride, to a solu- tion of mercurous nitrate. A white, curdy precipitate is obtained which is washed and dried. Properties. Prepared in the dry way calomel occurs as dense, fibrous, crystalline and slightly transparent masses, one side of which is smooth, the other presenting the sharp points of the crystals. When exposed to light, it becomes yellow and even gray in time, being partially decomposed. Its density is 380 ELEMENTS OP MODERN CHEMISTRY. 7.1 7. The density of its vapor is 8.35. It melts and vola- tilizes at the same temperature. When slowly sublimed, it crystallizes in square prisms. It is insoluble in water. A solution of potassium iodide agitated with calomel con- verts it into a green powder of mercurous iodide. If an excess of potassium iodide be employed, the green powder disappears and is replaced by a gray precipitate of metallic mercury, the mercurous iodide at first formed being decomposed into mercury and mercuric iodide, which dissolves in the potassium iodide. An analogous reaction takes place with the alkaline chlorides by the aid of heat, the mercurous chloride breaking up into mercuric chloride which dissolves, and metallic mercury which is deposited. MERCURIC CHLORIDE, OR CORROSIVE SUBLI- MATE. HgCl 2 Preparation. This body is obtained by double decomposi- tion, by heating a mixture of mercuric sulphate and sodium chloride on a sand-bath. The mercuric chloride condenses in the upper part of the matrasses which are imbedded up to the neck in the sand. HgSO 4 + 2NaCl Na 2 S0 4 -f HgCP Towards the close of the operation the heat is increased in order to agglomerate the sublimate by a partial fusion. Another process consists in passing chlorine into heated mercury ; the combination takes place with the production of luminous heat. Properties. Mercuric chloride prepared by the dry method occurs in compact, white, crystalline and friable masses, having a density of 6.5. It is an energetic poison. It melts at about 265, and boils towards 295. The density of its vapor is 9.42. By sublimation it may be obtained crystallized in rec- tangular octahedra. It is soluble in 19 parts of cold water, also in alcohol and ether. It is deposited from its hot, saturated, aqueous solution in long prisms, belonging to the type of the right rhombic prism. The crystals are anhydrous. The aqueous solution of mercuric chloride produces a white precipitate in a solution of albumen of white of egg. This MERCUROUS IODIDE MERCURIC IODIDE. 381 precipitate is a combination of mercuric chloride and albumen. Albumen is thus the antidote to corrosive sublimate. When a slight excess of ammonia is added to a solution of corrosive sublimate, a white deposit is formed, known as white precipitate, of which the composition is expressed by the formula HgH 2 NCl. HgCP + 2NH 3 = NH 4 C1 + HgH 2 NCl It may be regarded as the chloride of mercury-ammonium, that is, ammonium chloride in which 2 atoms of hydrogen are replaced by one atom of the diatomic metal mercury. Hg") HgH 2 NCl = H [ NCI H ) Corrosive sublimate forms crystallizable double combinations with the alkaline chlorides and with ammonium chloride. MERCUROUS IODIDE. HgI This compound is ordinarily prepared by directly combining mercury and iodine. 100 parts of mercury and 63.5 parts of iodine are triturated with a small quantity of alcohol, until the whole is converted into a green powder, which is then washed with boiling alcohol and dried. It may also be prepared by double decomposition by precipi- tating a solution of mercurous nitrate with potassium iodide, or by the reaction of the latter body upon calomel. Mercurous iodide is not a stable compound. It is decom- posed by light. Heat breaks it up into mercury and mercuric iodide, and the same decomposition is effected by potassium iodide and the alkaline chlorides. MERCURIC IODIDE. Hgl 2 Mercuric iodide is prepared by pouring a solution of 100 parts of potassium iodide into a solution of 80 parts of corro- sive sublimate. A beautiful scarlet-red precipitate of mercuric iodide is thrown down. It is necessary that the bodies be employed in the propor- 382 ELEMENTS OF MODERN CHEMISTRY. tions indicated ; an excess of potassium iodide would dissolve the mercuric iodide first precipitated. Mercuric iodide is almost insoluble in water ; it is slightly soluble in boiling alcohol, which deposits it on cooling in small red octahedral crystals. If mercuric iodide be heated in a small glass retort, it melts to a dark-yellow liquid which solidifies on cooling to a yellow mass. At a higher temperature the liquid boils and its vapor condenses in a dark-yellow liquid which solidifies to a yellow mass ; at the same time, right rhombic prisms of a yellow color sublime. If these be rubbed with a glass rod or other hard body they instantly become red, first at the point of contact, then throughout the entire mass. These two forms of mercuric iodide constitute one of the most curious examples of dimorphism. Mercuric iodide forms a combination with potassium iodide which is soluble in water. A solution of this iodo-hydrargyrate of potassium is not precipitated by potassium hydrate, but the liquid rendered alkaline by the latter reagent is a very sensi- tive test for ammonia (Nesslers test), with which it gives a pre- cipitate or a brown cloud more or less intense, according to the quantity of ammonia present. NITRATES OF MERCURY. Neutral mercurous nitrate (Hg 2 )"(N0 3 ) 2 -f 2H 2 0, is ob- tained by the action of an excess of cold, dilute nitric acid upon metallic mercury. After some time, short colorless prisms are formed in the liquid, constituting the neutral salt. The latter is readily soluble in water charged with nitric acid. When mercury is attacked by an excess of boiling nitric acid and the solution is evaporated, voluminous crystals of a basic mercuric nitrate separate, Hg(N0 3 ) 2 .HgO -j- 2H 2 O. The syrupy liquid from which these crystals are deposited, contains neutral mercuric nitrate. Hg(N0 3 ) 2 + 8H 2 This salt is deposited in large, colorless, rhombic tables when the syrupy solution is cooled to 15. A large quantity of cold water decomposes this nitrate into nitric acid which dissolves, and a basic salt, Hg(N0 3 ) 2 .2HgO -f- H 2 0, forming a yellow powder. SULPHATES OF MERCURY. 383 SULPHATES OF MERCURY. There is a mercurous sulphate, (Hg 2 )"S0 4 , and a mercuric sulphate, Hg"S0 4 . The first is obtained by heating equal parts of mercury and sulphuric acid, arresting the operation when two-thirds of the mercury are converted into a white, crystalline powder. Mer- curous sulphate is but slightly soluble in cold water. To prepare mercuric sulphate, 1 part of mercury and 1J parts of sulphuric acid are heated to complete desiccation on a sand-bath. Hg + 2H 2 S0 4 == 2H 2 + HgSO 4 + SO 2 It is well to add a small quantity of nitric acid before drying. Mercuric sulphate is an anhydrous, white powder. It decom- poses at a red heat into metallic mercury, sulphurous acid gas, and oxygen. Charcoal reduces it readily, equal volumes of carbon dioxide and sulphur dioxide being disengaged. Mercuric sulphate is slightly soluble in water : a large quan- tity of cold water converts it into a yellow, basic salt, HgSO 4 . 2HgO, known as turpeth mineral. Characters of Mercurous Salts. Their solutions are pre- cipitated black by hydrogen sulphide, and also by potassium hydrate and ammonia. Hydrochloric acid gives a white pre- cipitate which is blackened by ammonia. Potassium iodide forms a green precipitate of mercurous iodide, converted by an excess of the reagent into mercuric iodide which dissolves, and gray metallic mercury. Characters of Mercuric Salts. Solutions of mercuric salts are precipitated black by an excess of hydrogen sulphide, and by ammonium sulphide. Potassium hydrate forms a yellow precipitate, insoluble in excess. Ammonia yields a white precipitate in solutions of corrosive sublimate. Hydrochloric acid does not precipitate the mercuric salts. Iron, zinc, and copper precipitate metallic mercury from both mercurous and mercuric solutions. A slip of copper dipped into such solutions becomes covered with a gray coating which acquires brilliancy by rubbing. Heated with lime in a glass tube, all of the mercury com- pounds yield metallic mercury which sublimes in small globules, 384 ELEMENTS OF MODERN CHEMISTRY. easy to recognize under the microscope, and which can be char- acterized by the addition of iodine, the vapor of which converts the metallic globules into yellow or red mercuric iodide. SILVER Ag(Argentum) = 108 Natural State. Silver is found native and in combination in many minerals. Among these are the sulphide, the sulph- antimonides and sulpharsenides, the antimonide, chloride, bro- mide, iodide, selenide, telluride, and lastly an amalgam of silver. It is found in small proportions in many galenas and copper pyrites. Treatment of Silver Ores. The silver is extracted from galena by first reducing the lead, and then submitting the argentiferous lead obtained to cupellation (page 359). Silver ores free from lead are treated by a peculiar process called amalgamation , since it is based upon the employment of metallic mercury which dissolves silver ; the amalgam of silver formed is decomposed by heat. Several processes are employed for the chlorination and amalgamation of silver. Freiberg Amalgamation Process. The Freiberg silver ore is poor, containing only two or three thousandths of silver in the form of sulphide, disseminated through iron and copper pyrites. The ore is pulverized, mixed with one-tenth its weight of common salt, and roasted in a reverberatory furnace. The sulphides are oxi- dized, with disengagement of sul- phurous acid gas and formation of sulphates. The latter react upon the sodium chloride, forming sodium sulphate and metallic chlorides : all of the silver is thus converted into chloride. The product of the roast- ing is reduced to powder, washed, and introduced, together with water and scrap-iron, into amal- gamation barrels, which are rotated by water-power (Fig. 116). When the mixture has become homogeneous, mercury is added FIG. 116. SILVER. 385 FIG. 117. and dissolves the silver set free by the action of the iron upon the silver chloride ; it also dissolves a small quantity of copper formed by the reduction of cuprous chloride present. After the barrels have been rotated for some hours, the amalgam is collected and compressed in canvas bags, through which the excess of mercury, alloyed with a very small quantity of foreign metals, passes, while a pasty . f . amalgam of silver and copper remains in the bags. This amalgam is put into iron cups, bb (Fig. 117), set upon an iron rod on a tripod base, a, standing in a vessel of water. The whole is cov- ered with a bell-shaped iron hood which dips into the water, and the upper part of which is surrounded by burning coals. The mercury volatilizes and condenses in the cold water, and an alloy of silver and copper, containing about 28 per cent, of the latter metal, as well as small quantities of lead, antimony, etc., remains in the cups. It is purified either by cupellation or by refining. Cupellation consists in melting the impure silver with lead, as has been already described. In refining, the silver is melted in a hemispherical iron vessel lined with a thick layer of marl and wood ashes. It is a porous cupel, which absorbs the oxides formed by the action of the air upon the lead and copper alloyed with the silver ; the latter remains in the cupel at the close of the operation in a pure state. Mexican Amalgamation Process. American silver ore con- sists of sulpharsenide and sulphantimonide of silver, mixed with silver chloride and native silver, the whole being disseminated in silica, calcium carbonate, and ferric oxide. In Mexico, the following primitive process is still used. The finely-pulverized ore is mixed with two per cent, of common salt and thrown into circular areas paved with flag-stones, where it is rendered homogeneous by being trodden for several hours by mules. About one per cent, of copper pyrites which has been roasted in the air and contains cupric sulphate is then added. The latter salt reacts with the sodium chloride, forming sodium sul- phate and cupric chloride, which latter decomposes the silver sulphide, forming silver chloride and cupric sulphide. Mer- B 33 386 ELEMENTS OP MODERN CHEMISTRY. cury is then added and reduces the silver chloride, with for- mation of chloride of mercury and metallic silver. During the whole time the mass is continually trodden by the mules, and the mercury comes in contact with the disseminated silver : the amalgam formed solidifies in about a fortnight. A second and finally a third addition of mercury is then made until 7 or 8 parts of that metal have been employed for one part of silver to be extracted. After a few months, the operation is termi- nated, and the mass is washed with large quantities of water to remove the earthy and salty matters. The amalgam remains, and is heated in order to extract the silver. American Process. The above method of extraction is too slow to be employed for the vast quantities of silver ore that are mined on the Pacific Slope. The ore is there crushed and roasted with sodium chloride and a small proportion of cupric sulphate, in furnaces of a peculiar construction. By this means all of the silver is converted into chloride. The mass is made into a pulp with water and agitated with mercury in large tanks or vats. The silver chloride is reduced as before, and the amalgam obtained is first squeezed out and afterwards heated in iron retorts to expel the mercury. Properties. Silver is the whitest and most brilliant of all the ordinary metals. Next to gold, it is the most malleable and the most ductile. Its density is 10.5. It melts towards 1000, and when fused has the curious property of dissolving oxygen, of which it absorbs 22 times its volume. On solidifying, it again disengages the gas ; this phe- nomenon, which occasionally causes the projection of portions of silver, is called spitting. Silver volatilizes at the high tem- perature of the oxyhydrogen blow-pipe. It is unaltered by the air. It absorbs ozone, being converted into the dioxide Ag 2 2 . It combines with hydrogen dioxide, forming argentous and argentic hydrates (Weltzien). It decomposes concentrated solution of hydriodic acid, dis- engaging hydrogen and forming silver iodide (Deville). Hy- drochloric acid only attacks it superficially. Hydrogen sulphide blackens it, forming a pellicle of silver sulphide. Its best sol- vent is nitric acid which attacks it in the cold, yielding silver nitrate and disengaging red vapors. The alkalies have no action upon silver; for this reason, silver vessels are used for fusing potassium hydrate and concentrating its solution. SILVER SULPHIDE SILVER CHLORIDE. 387 SILVER OXIDE. Ag'O The only important oxide of silver is the monoxide, which is precipitated in the anhydrous state when potassium hydrate, free from chloride, is added to a solution of silver nitrate. It forms an olive-brown, flocculent deposit which yields a brown powder on drying. Silver oxide is readily decomposed by heat into silver and oxygen. It is reduced by hydrogen at a temperature below 100. When recently precipitated, it is slightly soluble in water. It is an energetic base, perfectly neutralizing the acids, and displacing cupric oxide from the cupric salts. When oxide of silver is digested with ammonia it is con- verted into a very explosive, black powder, known as fulmi- nating silver. Its composition is not yet well known. SILVER SULPHIDE. Ag 2 S To the oxide of silver corresponds the sulphide Ag 2 S, which occurs native, crystallized in regular octahedra, ordinarily mod- ified by facettes. It is soft and can be scratched by the finger- nail. Silver and sulphur also combine readily by the aid of heat. SILVER CHLORIDE. AgCl This body is found native and is known to mineralogists as horn-silver. It is sometimes found crystallized in cubes and octahedra. It is formed directly when silver is heated in chlo- rine gas, and is prepared by double decomposition by adding hydrochloric acid or a solution of sodium chloride to solution of nitrate of silver. A white, curdy precipitate is thus obtained, which assumes a violet tint when exposed to the action of light. The change of color is due to partial decomposition. Silver chloride melts at about 260, and solidifies on cooling to a gray, horn-like mass that can be cut with a knife. If recently precipitated and moist silver chloride be placed upon a sheet of zinc, in a short time a dark color will appear on the borders of the chloride, and the whole of that body will 388 ELEMENTS OF MODERN CHEMISTRY. soon be converted into a dark-gray powder of finely-divided silver. Zinc chloride is at the same time formed. This reaction takes place much more rapidly if the silver chloride be moistened with hydrochloric acid. In this case the reduction is effected by nascent hydrogen produced by the action of the hydrochloric acid on the zinc. When silver chloride is fused with the alkaline hydrates or carbonates, it is reduced to metallic silver : oxygen is disen- gaged, and an alkaline chloride is formed. Recently-precipitated silver chloride dissolves readily in aque- ous ammonia. When dry, it absorbs ammonia gas abundantly, and Faraday employed this compound for the preparation of liquid ammonia. Silver chloride dissolves also in solutions of the alkaline hyposulphites. SILVER IODIDE. Agl Silver iodide is obtained as a yellow precipitate by adding potassium iodide to a solution of silver nitrate. It blackens on exposure to light. It is but very slightly soluble in ammo- nia, a property which distinguishes it from silver chloride. SILVER NITRATE. AgNO This salt is prepared by dissolving silver in nitric acid. If the metal be pure, a colorless solution is obtained which after concentration and cooling deposits large, colorless tables of an- hydrous silver nitrate. If silver coin be employed, the solution will be blue, containing, independently of silver nitrate, cupric nitrate. The latter may be removed by evaporating the residue to dryness and carefully heating it, so that the salt may remain fused for some time. The cupric nitrate is decomposed, while the silver nitrate remains mixed with cupric oxide, from which it may be freed by solution and filtration. Fused silver nitrate constitutes lunar caustic. This salt dissolves in its own weight of cold, and in half its weight of boiling water. The solution is neutral to test-paper. When exposed to the air, it blackens, as do also the crystals and the fused salt, by reason of a partial reduction due to the organic matters suspended in the air. ASSAYING OF SILVER. 389 It blackens the skin from a similar cause. Hydrogen slowly reduces the solution of silver nitrate with deposition of metallic silver (Beketoff). Characters of Silver Salts. Solutions of the silver salts are precipitated black by hydrogen sulphide and by ammonium sulphide. Potassium hydrate forms an olive-green precipitate of silver oxide, insoluble in excess. Ammonia does not precipitate them. Hydrochloric acid and the soluble chlorides form a white precipitate of silver chloride, insoluble in either cold or boiling nitric acid, but soluble in ammonia. Potassium iodide gives a yellow precipitate, almost insoluble in ammonia. Silvering. This operation consists in covering the common metals or glass with a coating of silver more or less thick. The metals are silvered by either amalgamation or galvanic deposition. In the latter and preferable operation, a solution of the double cyanide of silver and potassium is generally used. Mirrors and glass articles in general are silvered by the re- duction of a silver salt by aldehyde, glucose, or tartaric acid. The following receipt is given by Liebig: a solution of 10 grammes of silver "nitrate is supersaturated with ammonia and rendered strongly alkaline by caustic soda. The volume of the liquid should be 1450 c.c. Another solution is prepared by dissolving 1 part of milk sugar in 10 parts of water. The latter solution is mixed with its own volume of the first solu- tion, and the glass to be silvered is washed with alcohol and immersed in the liquid. The reduction of the silver salt begins immediately, and does not require the aid of heat. The experiment may easily be made in a glass flask, the interior of which will be uniformly silvered. Assaying of Silver. This name is applied to the methods which serve for the analysis of alloys of silver and copper, such as coin, medals, silverware, and jewelry. The assay may be conducted by the dry way or by the wet way. The dry assay consists in the operation called cupellation (Fig. 118). A certain quantity of metallic lead is melted in a cupel of bone-ash in a reverberatory furnace, and a weighed quantity of the alloy of silver and copper, carefully wrapped in a small piece of paper, is placed upon the fused metal. The silver dissolves in the melted lead, and a ternary alloy is thus obtained which is exposed to the action of air at a red heat. 33* 390 ELEMENTS OP MODERN CHEMISTRY. Under these conditions, the lead and copper become oxidized ; the oxide of lead fuses, and the melted litharge, which should be in great excess in proportion to the oxide of copper, dis- solves the latter, and with it is absorbed by the porous cupel. The phenomenon of brightening (page 360) indicates the ter- mination of the process. FIG. 118. The wet assay, invented by Gay-Lussac, consists in adding to a solution in nitric acid of a known weight of the alloy of silver and copper, a titered solution of sodium chloride, that is, a solution containing an exactly known weight of salt in one litre of water. This solution is cautiously added until it no longer precipitates silver chloride, and the quantity of silver present is calculated by the volume of the titered solution that has been required to completely precipitate the silver in the form of chloride. As the latter readily deposits from a liquid that is carefully agitated, it is easy to catch the termination of the operation, that is, the precise moment when all of the silver is precipitated and the addition of the titered liquid must be arrested. GOLD. 391 Process. Two titered solutions are used to precipitate the silver: 1st, a normal solution, containing 0.5417 gramme of sodium chloride per decilitre, a quantity sufficient to precipitate one gramme of silver ; 2d, a decinormal solution, that is, one containing the same quantity of sodium chloride per litre, so that 1 c.c. of this liquid will precipitate one milligramme of silver. To analyze an alloy of silver, a coin, for example, such a quantity is weighed as would contain one gramme of silver, if the proportion of silver were a little less than the extreme limit allowed. If the alloy ought to contain 900 thousandths of pure silver, with a tolerance of 2 thousandths, it would be rejected should it contain only 897 thousandths. We suppose, however, that the latter is its quality, and weigh a quantity of the alloy which would then contain one gramme of pure silver, that is, 1.1148 grammes. This alloy is dissolved in nitric acid, and one decilitre of the normal solu- tion is added. All of the silver should not be precipitated, for the standard of the alloy should be above 897. This is deter- mined by adding to the clarified liquid one or more cubic cen- timetres of the decinormal solution, until the liquid ceases to be troubled by a fresh addition. As each cubic centimetre of this solution corresponds to one milligramme of silver, we must add to the gramme of silver at first precipitated as many milligrammes as we have added cubic centimetres of the deci- normal solution, the last cubic centimetre added counting for only half a milligramme. Knowing the quantity of pure silver contained in 1.1148 grammes of the alloy analyzed, the standard of the latter is determined by a simple calculation. GOLD. Au(Aurum) = 197 Natural State. Gold is one of the most anciently known metals. It is generally found in the native state, either in streaks or veins, or in sand. It ordinarily occurs in scales or rounded grains disseminated in alluvial sands, or in the rocks whose disintegration produces such sands. It is well known that gold-dust is suspended in the waters of certain rivers. Gold is sometimes found combined with silver, lead, copper, and tellurium. 392 ELEMENTS OF MODERN CHEMISTRY. Extraction. Gold is extracted from auriferous sand by washings, which remove the particles lighter than the gold. These washings are conducted in wooden troughs (cradles), or on inclined tables, the gold sinking to the bottom of the cradles or remaining on the tables. When it is in particles too minute to be separated mechanically from the sand, which still remains in small quantity, the whole is agitated with mercury ; the gold dissolves. The amalgam thus obtained is compressed in a chamois-skin, which allows the passage of the excess of mer- cury. When the solid residue is distilled the gold remains. Auriferous quartz rocks are crushed to powder, which is then subjected to washings. Mercury is sometimes employed to ex- tract the gold from the pulverized rock. The following process has been employed for some years in California and Australia. The crushed rock, with mercury, water, and two cast-iron balls, is introduced into basins, to which a rotating motion is given (Fig. 119). By the friction of the balls it is soon reduced to FIG. 119. an impalpable powder, which remains suspended in the water, and is carried out with the latter through openings in the upper part of the basins, while the gold amalgamates with the mer- cury. Native gold, as well as that extracted from different minerals, is nearly always alloyed with silver. The two metals are sep- arated by the wet way, by attacking the alloy with either nitric or sulphuric acid. Nitrate or sulphate of silver is formed, the latter being soluble in hot water. The gold remains in a pul- verulent state. It is to be remarked that the alloy of gold and silver must be rich in silver in order that this process, called refining, can be applied. Hence it is sometimes necessary to OXIDES OF GOLD CHLORIDES OF GOLD. 393 increase the proportion of silver by melting the alloy with that metal. An alloy of gold and silver rich in gold may also be treated with aqua regia. Both metals are converted into chlorides; that of silver is insoluble, while that of gold dissolves. When ferrous sulphate is added to the yellow solution of chloride of gold, a precipitate of metallic gold is obtained, the chlorine acting upon the iron of the ferrous sulphate which is thus transformed into ferric salt. Properties of Gold. Pure gold has a beautiful yellow color. In thin leaves it is translucent, allowing the passage of a green- ish light. Its density is 19.5. It is quite soft, and is the most malleable and most ductile of the metals. It melts at 1200, and volatilizes at a higher temperature. Its vapor is green. It is unaltered by the air at all temperatures. Sulphuric, hydrochloric, nitric, and phosphoric acids have no action on it either in the cold or when aided by heat. It is dissolved by nitro-hydrochloric acid. Some gold leaf may be boiled with hydrochloric acid in a test-tube ; the gold will resist the action of the acid, and will retain its lustre. Some more gold leaf may be boiled with pure nitric acid in another tube, and again the metal will not be attacked. But on mixing the two liquids, the gold will be dis- solved with disengagement of red vapors. Gold trichloride will be formed, and will color the liquid yellow. OXIDES OF GOLD. There are two compounds of gold and oxygen, a monoxide, Au 2 0, and a trioxide, Au 2 3 . The latter forms compounds with the bases. When magnesia is added to solution of auric chloride, an insoluble yellow precipitate of magnesium aurate is formed ; when this is decomposed by nitric acid it leaves auric hydrate. This hydrate is yellow ; it easily parts with its water, and is converted into a brown-black powder of auric oxide. The latter is not stable, being decomposed by light and by a temperature of about 250. CHLORIDES OF GOLD. Aurous chloride, AuCl, is obtained as an insoluble yellow powder by heating auric chloride to 230. B* 394 ELEMENTS OF MODERN CHEMISTRY. Auric chloride or trichloride of gold, AuCP, is prepared by dissolving the metal in aqua regia. After concentration the liquid solidifies, on cooling, to a dark-red, crystalline and deli- quescent mass. The solution of auric chloride is yellowish-brown when con- centrated, pure yellow when dilute. It is decomposed by light. It colors the skin violet, and is reduced by a great number of bodies. Phosphorus, and hypophosphorous, phosphorous and sulphurous acids precipitate from it metallic gold. It is the same with most of the metals, which combine with the chlorine, setting free the gold. A brown precipitate of metallic gold is immediately obtained on adding a solution of ferrous sulphate to a solution of auric chloride. Auric chloride dissolves in ether, which removes it from its aqueous solution when the two liquids are agitated together. If a solution of auric chloride be added to a mixture of stannous and stannic chlorides in solution, a flocculent precipi- tate of a purple color, more or less pure according to the con- centration of the solutions and the proportions of the mixture, will be formed. It is purple of Cassius, a compound employed in painting on glass and porcelain. It contains tin, gold, oxy- gen, and hydrogen, but its constitution is not well known. Auric chloride forms crystalline compounds with the alkaline chlorides. When a mixture of chloride of gold and sodium chloride is evaporated until a pellicle forms on its surface, yellow crystals containing NaCl. AuCP -J- 2H 2 O, are formed on cooling. Gilding. Several processes are used for gilding metals, such as silver and copper. The objects may be gilded by amalga- mation, by dipping, or by galvanic deposition. Gilding by Amalgamation. Grold readily alloys with mer- cury, and the amalgam is used for gilding objects of silver and copper. The pieces are heated to destroy greasy matters, and are then cleaned by dipping them into dilute sulphuric acid, after which they are washed and dried with saw-dust. They are then rubbed with a brush of brass wires dipped into a solu- tion of mercurous nitrate, and then with a brush impregnated with an amalgam of one part of gold and eight parts of mer- cury. They are afterwards heated to volatilize the mercury, an operation dangerous to the health of the workmen, and which should be conducted in a furnace having a good draught. The pieces thus gilded are dull ; they become lustrous after suitable washings and polishings. PLATINUM. 395 Gilding by Dipping. Copper objects may be covered with a thin film of gold by dipping them into a boiling solution of carbonate and phosphate of sodium to which auric chloride has been added. Electro- Gilding. The copper objects, previously heated and cleaned by dilute sulphuric acid, are plunged for a few seconds into dilute nitric acid and then wiped dry. They are then connected with the negative pole of a battery and dipped into a bath composed of 1 ( part of cyanide of gold, 10 parts of potas- sium cyanide, and 100 parts of water. A plate of gold plunged into the same bath constitutes the positive pole. When the current passes, the objects become covered with a uniform and adherent coating of gold. As the metal is precipitated from the solution, it is replaced by an equivalent quantity from that which constitutes the positive pole, and which dissolves. The bath thus retains a constant composition. The same process is applicable to electro-silvering. Assaying of Gold Alloys. Gold is assayed by cupellation. The alloy is first melted with silver, so that the quantity of the latter metal present may be at least triple that of the gold. This alloy is submitted to cupellation, an operation which presents no difficulty, for gold rich in silver does not spit. The button is hammered out to a thin sheet, reheated and formed into a little cornet, which is introduced into a small flask and heated with nitric acid of 22 Baume. After several minutes' boiling the greater part of the silver is dissolved ; the liquid is then decanted and replaced by more concentrated nitric acid. All of the silver dissolves and the gold remains in the form of a but slightly coherent cornet. It is washed, heated to redness in a crucible to give it coherence, and finally weighed. PLATINUM. Pt = 107.5 Natural State and Treatment of Platinum Ores. Plat- inum is found native, generally in alluvial sands. Its principal deposits are in the Ural Mountains, Brazil, and New Granada. The platinum ore, extracted from the sand by washing, contains, independently of 73 to 86 per cent, of platinum, various other metals, such as iridium, palladium, rhodium, osmium, ruthenium, gold, iron, and copper; an alloy of osmium and iridium, and 396 ELEMENTS OF MODERN CHEMISTRY. various minerals, such as titaniferous iron, chrome iron, pyrites, etc. The ore is well washed to remove the sand, and treated with dilute aqua regia which dissolves the gold, iron, and cop- per; it is then heated with concentrated hydrochloric acid and nitric acid is gradually added. The aqua regia dissolves the platinum and certain of its accompanying metals, leaving the osmium and iridium. The solution is neutralized with sodium carbonate and treated with a solution of cyanide of mercury, which precipitates palladium cyanide. A solution of ammo- nium chloride is added to the filtered liquid, and forms an abundant precipitate of ammonium and platinum double chlo- ride, which is generally mixed with a small quantity of ammo- nium and iridium double chloride. This precipitate is calcined at a dull-red heat, and leaves a dull-gray, spongy residue. It is spongy platinum. It contains a small quantity of iridium. To give coherence to this sponge and convert it into a mal- leable and ductile metal, it is reduced to powder in a wooden mortar and triturated with enough water to convert it into a perfectly homogeneous paste. This paste is introduced into a slightly-conical cylinder of brass or iron, and compressed first with a wooden piston, then by a steel rod. The compression is finished by the aid of a hydraulic press, and the slightly- conical cylinders so formed are heated to whiteness and forged under the hammer, as iron is forged. H. Sainte-Claire Deville and Debray have recently extracted the metal by simple fusion of the ore. The fusion is effected in a lenticular cavity cut in two large masses of quick-lime, placed one above the other. A current of illuminating gas is directed into this furnace, and the combustion is supported by a continual supply of oxygen. Properties of Platinum. Platinum has a grayish-white lustre. It melts only at the highest attainable temperatures. The density of the cast metal is 21.1 ; that of the forged metal 21.5. It softens at a white heat, and can then be forged and welded like iron. The experiments of H. Deville and Troost have shown that a red-hot platinum tube allows hydrogen to pass through its pores. Platinum has the curious property of condensing gases on its surface, and this property is the cause of certain chemical phe- nomena that were formerly attributed to mere contact of the metal. If a morsel of platinum-sponge be introduced into a small CHLORIDES OF PLATINUM. 397 jar filled with an explosive mixture of oxygen and hydrogen, the gases will combine instantly, with explosion. This property is most highly developed in platinum-black, for in this form the metal exists in an extreme state of division. It may be prepared by reducing a solution of platinic chloride by zinc ; or platinum dichloride may be boiled with potassium hydrate, and alcohol or a solution of sugar gradually added to the liquid, which must be continually stirred. The platinum is precipitated as a black powder. Platinum is unaltered by the air. It is not attacked by either nitric, hydrochloric, or sulphuric acids, even boiling. ^ It dissolves in aqua regia. The alkaline hydrates attack it at high temperatures on contact with the air. It is the same with the alkaline nitrates. There are two oxides of platinum, a monoxide, PtO, and a dioxide, PtO 2 . CHLORIDES OF PLATINUM. These are the more important compounds of platinum. There are two, a dichloride, PtCl 2 , and a tetrachloride, PtCl*. Platinum dichloride is obtained by cautiously heating the tetrachloride to 200 D . Chlorine is disengaged, and after cool- ing, the residue is exhausted with boiling water, which leaves an olive-green powder, constituting the dichloride. When ammonia is added to a solution of platinum dichloride in hydrochloric acid, a green, crystalline powder separates after some time. It is called green salt of Magnus, and contains PtCl 2 -f 2NH 3 It maybe regarded as the dichloride of platinoso-diammonium. Pt" H2 H 2 It is derived from two molecules of ammonium chloride by the substitution of an atom of diatomic platinum for two atoms of hydrogen. Platinum tetrachloride, or platinic chloride, PtCl 4 , is formed when platinum is dissolved in aqua regia. A red- brown solution is obtained, which, after concentration and cool- ing, deposits red-brown needles of hydrated platinic chloride. 34 398 ELEMENTS OP MODERN CHEMISTRY. The crystals lose their water when heated, and are converted into a dark, red-brown mass, which constitutes the anhydrous chloride PtCl*. This body absorbs moisture when exposed to the air. It is very soluble in water, alcohol, and ether. If a solution of ammonium chloride be added to a solution of platinic chloride, a yellow, crystalline precipitate of plati- num and ammonium double chloride is immediately formed. This body is but little soluble in cold water, but more soluble in boiling water, from which it is deposited in microscopic, regular octahedra. It is almost insoluble in alcohol. It contains PtCl 4 .2NH 4 Cl A yellow, crystalline precipitate of double chloride of plati- num and potassium is obtained, in the same manner, on adding a solution of platinic chloride to a solution of a potassium salt, if the liquids be not too dilute. PtCl 4 .2KCl ORGANIC CHEMISTRY. GENERAL IDEAS UPON THE CONSTITUTION OF ORGANIC COMPOUNDS. ORGANIC CHEMISTRY studies the history of the compounds of carbon. The most simple of these are the gases carbon monoxide and carbon dioxide ; each contains but a single atom of carbon. In this respect they resemble the inflammable gas which is disengaged from the mud of marshes ; it contains one atom of carbon combined with four atoms of hydrogen. The gas hydrogen dicarbide or ethylene, which has already been mentioned, contains two atoms of carbon united with four atoms of hydrogen. A great number of compounds are known which contain only carbon and hydrogen, and they are called hydrocarbons or carburetted hydrogens. The atoms of carbon are aggregated in them, together with the atoms of hydrogen. Other elements are often added to the preceding, forming molecules more or less complex. The carbon atoms form as it were the framework, and the carbon compounds possess pecu- liar properties precisely on account of the easy facility with which the atoms of carbon accumulate in one and the same molecule, and link themselves in some manner one to another. The following developments will give some idea of the mode of generation and the structure of organic molecules. The most Simple Organic Compounds. Their Composi- tion proves Carbon to be a Tetratomic Element. The most simple of the hydrocarbons is marsh gas. When this gas is submitted to the action of chlorine, one or more atoms of hydrogen may be removed from it ; they com- bine with the chlorine and are disengaged in the form of hy- drochloric acid gas. The curious fact, first noticed by Dumas, is then observed, that each atom of hydrogen which is removed is replaced by an atom of chlorine. This substitution gives 400 ELEMENTS OF MODERN CHEMISTRY. rise to a series of chlorinated compounds, which present the most simple relations with marsh gas. The latter contains only carbon and hydrogen. The chlorine compounds derived from it by substitution, form with it the following series : CH* marsh gas, or methane. CH 3 CI monochloromethane (methyl chloride). CH 2 C1 2 dichloromethane (methylene chloride). CHC1 3 trichloromethane (chloroform). CC1 4 tetrachloromethane (carbon tetrachloride). In each of these compounds a single atom of carbon is united with four monatomic atoms. We have seen that the atoms of chlorine and hydrogen are equivalent as regards their power of combination. In the preceding compounds, the sum of the atoms of hydrogen and chlorine which are combined with one atom of carbon is invariably four, and this number cannot be exceeded. But two atoms of a monatomic element may be re- placed by one atom of a diatomic element. One atom of car- bon, which unites with four atoms of hydrogen or chlorine, may unite with two atoms of oxygen to form carbon dioxide CO" 2 and this compound is saturated like those preceding, for ono atom of oxygen is equivalent to two atoms of hydrogen or chlorine. In carbon monoxide, CO", the affinity of carbon is not satisfied ; hence this gas will unite directly with an atom of oxygen to form carbon dioxide, or with two atoms of chlo- rine to form chloro-carbqnic gas. CO"CP In ammonia, one atom of nitrogen is combined with three atoms of hydrogen ; nitrogen is triatomic ; hence it may replace three atoms of hydrogen. A body is known which represents marsh gas, in which three atoms of hydrogen are replaced by one atom of nitrogen. This is the dangerous poison known as prussic or hydrocyanic acid, and the composition of which is represented by the formula CN'"H In all of the compounds which have just been mentioned a single atom of carbon is invariably united to a number of ele- ments of which the united atomicities is always four, and never more nor less than that number. It is then reasonable to conclude that in them carbon plays the part of a tetratomic INTRODUCTION TO ORGANIC CHEMISTRY. 401 element. This important fact, first exposed by Kekule, can be clearly understood if we represent the preceding atomic formulae in a graphic manner, that is, by symbols so arranged as to show the reciprocal relations of the atoms and their mutual satura- tion. In these formulae a saturated atomicity is indicated by a line of union, two atomicities by two lines, etc. H H H Cl H-C-H H-C-C1 C1-C-C1 C1-6-C1 4 A Marsh gas. Monochloro- Trichloromethane. Carbon methane. (Chloroform.) tetrachloride. Cl o=c=o ci-dtp H-C_-N Carbon dioxide. Chlorocarbonic gas. Hydrocyanic acid. There exists a very volatile, ethereal liquid, which represents marsh gas, in which one atom of hydrogen is replaced by iodine. It is the body known as methyl iodide, CH 3 I. If this body be heated for a long time in a sealed tube with a solution of potassium hydrate, potassium iodide will be grad- ually formed, and the solution will contain a volatile, spirituous liquid which can easily be separated by distillation, for it boils at 66. It is the same body which constitutes the most vola- tile of the liquids which are formed in the destructive distilla- tion of wood ; it is called wood spirit, and its chemical name is methylic alcohol. The reaction by which it is formed is very simple. The iodine of the methyl iodide combines with the potassium ; but when this iodine is removed, the carbon remains united to but three atoms of hydrogen. It is no longer saturated, and it therefore combines with the oxygen and hydrogen which were united with the potassium in the potassium hydrate. CH 3 I + KOH = CH 8 .OH + KI It will be seen that the atom of oxygen alone does not com- bine with the group CH 3 , which is called methyl. It is accom- panied by an atom of hydrogen, with which it remains united in the new compound which is called methyl hydrate or methylic alcohol. As has been said, this oxygen replaces the iodine in the iodide of methyl, but as it possesses two atomici- ties, and the carbon already united with H 3 has only one free atomicity, the atom of oxygen can only fix upon the carbon by 34* 402 ELEMENTS OP MODERN CHEMISTRY. one of its atomicities ; the other remains saturated by the atom of hydrogen. The latter is then drawn into the combination, and is united, not to the carbon, but to the oxygen. The reaction takes place as if the atom of iodine were replaced by the group hy- droxyl (OH) which is monatomic. Hence the relations between the atoms in methyl hydrate are represented by the formula H H-t-(OH)' H If we compare the constitution of the three bodies CH 3 C1, CH 3 I, CH 3 (OH), we notice that they contain a common ele- ment, namely, the group CH 3 , which is united to chlorine, to iodine, or to hydroxyl. Besides this, experiment has shown us that methyl iodide can be transformed into hydrate. The group methyl hence presents a certain stability and can pass from one combination to another. This is expressed by saying that it is a radical. If methyl iodide be heated with an aqueous solution of ammonia, among the products formed will be found the hydri- odide of a base which represents ammonia in which one atom of hydrogen is replaced by the group methyl. Potassium hydrate sets this base at liberty. At ordinary temperatures and pressures, it constitutes a gas, very soluble in water and possessing a strong ammoniacal odor. It is methylamine. The reaction by which it is formed is as follows : the iodine with- draws one atom of hydrogen from the ammonia, which atom of hydrogen is replaced by the group CH 3 . CH 3 I + NH 3 == CH 3 (NH 2 ).HI. Methylamine hydriodide. In methylamine then, the fourth atomicity of the carbon atom is saturated by nitrogen, but as this element is triatomic it brings into the combination two atoms of hydrogen which saturate its two other atomicities. It may then be said that in methylamine the fourth atomicity of carbon is saturated by the group NH 2 . This is expressed in the following formulae. H II H-C-N=H 2 = H-C-(NH 2 )' H H Methylamine. INTRODUCTION TO ORGANIC CHEMISTRY. 403 Generation of Hydrocarbons containing Several Atoms of Carbon. The preceding compounds contain but a single atom of carbon, but starting with one of these compounds we may produce more complicated organic molecules containing several carbon atoms. If methyl iodide be heated with sodium in sealed tubes, sodium iodide is formed, and a gas, a hydrocarbon, is confined under great pressure in the tubes. This gas escapes, and may be collected, when the drawn-out points of the tubes are opened in the blow-pipe flame. It is dimethyl, and has been formed according to the following reaction : 2CH 3 I -f Na 2 = C 2 H 6 + 2NaI Methyl iodide. Dimethyl, or ethane. Two molecules of methyl iodide have entered into the reac- tion, and the whole of the carbon of these two molecules is found in one molecule of the hydrocarbon, C 2 H 6 = (CH 3 ) 2 , which results. On losing their iodine the two methyl groups combine to- gether. One of the carbon atoms attracts the other, exchanging with it the fourth atomicity set free by the loss of the iodine. Hence the iodine of one of the molecules of methyl iodide has been replaced by the carbon of the other, which fixes upon the group CH 3 by a single one of its atomicities, and at the same time brings into the combination the three atoms of hydrogen which saturate the other three atomicities. This is expressed in the following formulae : H H H H H-C-H H-C-I H-C-C-H i i ii H H HH Methane (methyl hydride). Methyl iodide. Dimethyl (ethyl hj'dride or ethane). The mode of generation of this new hydrocarbon, which contains two atoms of carbon, is worthy of consideration. It results from the substitution of a methyl group for one atom of hydrogen in methyl hydride. One atom of carbon, accompa- nied by three atoms of hydrogen, fixes upon another atom of carbon of which it completes the saturation. By this exchange of atomicities each of the carbon atoms retains only three affin- ities which are satisfied by three atoms of hydrogen. The two methyl groups, CH 3 -f- CH 3 = C 2 H 6 , are then united by their carbon atoms, and are held together by the affinity of 404 ELEMENTS OP MODERN CHEMISTRY. carbon for carbon. In methyl hydrate the group hydroxyl is bound to the group CH 3 by the affinity of carbon for oxygen. In methylamine, the group NH 2 is united to the group CH 3 by the affinity of carbon for nitrogen. In dimethyl, it is carbon which is united to carbon. This has before been expressed by saying that the atoms of this element possess a faculty to accu- mulate in one and the same molecule. It is in this curious property that must be sought the reason for the existence of those innumerable compounds, more or less rich in atoms of carbon, which constitute the immense field of organic chemistry. But it is important to study by new examples this mode of formation of organic compounds. Dimethyl, which we have seen is produced by the action of sodium upon methyl iodide, is also known as ethyl hydride. If one of its atoms of hydrogen be replaced by an atom of chlo- rine, ethyl chloride, C 2 H 5 C1, is obtained. Ethyl iodide, C 2 H 5 I, represents ethyl hydride, in which one atom of hydrogen has been replaced by iodine. If a mixture of methyl iodide and ethyl iodide be heated with sodium, among the products of the reaction will be found a gas containing C 3 H 8 ; it is the methylide of ethyl, resulting from the combination of methyl, CH 3 , with the group ethyl, C 2 H 5 . It represents ethyl iodide in which the atom of iodine has been replaced by a methyl group, the carbon of the latter group being fixed by one of its atomicities to one of the carbon atoms of the group C 2 H 5 . In the same manner, by heating a mixture of propyl iodide, C 3 H 7 I, and methyl iodide with sodium, we may add to the propyl group, C 3 H 7 , a new atom of carbon escorted by its three atoms of hydrogen. HH HHH HHHH ii ill i i i i H-C-C-I H-C-C-C-H H-C-C-C-C-H, etc. ii ill i i i i HH HHH HHHH Ethyl iodide. Methyl-ethyl (propane). Methyl-propyl (butane). Nothing prevents the continuation of these additions of car- bon to incomplete hydrocarbons, that is, to the residues of the subtraction of iodine from the saturated iodides, of which the following are the names and formulae : CH 3 I C 2 H 5 I C 3 H 7 I C 4 H 9 I C 5 H U I, etc. Methyl iodide. Ethyl iodide. Propyl iodide. Butyl iodide. Amyl iodide. INTRODUCTION TO ORGANIC CHEMISTRY. 405 The following hydrocarbons would then be formed succes- sively : C 2 H 5 -CH C 8 H*-CH3 C*H 9 -CH C 5 H ll -CH 3 , etc, Methyl-methyl Methyl-ethyl Methyl-propyl Methyl-hutyl Methyl-amyl (Ethane). (Propane). (Butane). (Pentane). (Hexane). In all of these cases, the atoms of carbon united together form, as it were, a continued chain, and the atoms of hydrogen are grouped around them as satellites. Homologous Bodies. Very simple relations exist between the hydrocarbons of which we have just studied the mode of formation. They form a series of which each member differs from the preceding by the addition of CH 2 . These relations will appear clearly if the formulae already given be replaced by the crude formulae : CH 4 methane. C 2 H 6 ethane. C 3 H 8 propane. C 4 H 10 butane. C 5 H 12 pentane. This group of hydrocarbons constitutes what is called the homologous series of marsh gas, or the series C"H 2n+2 . Many other series are known, the terms of which are related to each other in the same manner, and the bodies which form part of them may present the greatest differences in composition. Sometimes they contain only carbon and hydrogen. Again, they may contain oxygen or nitrogen in addition to these ele- ments ; in this case the former elements are united to carbon by one or more of their atomicities, as has already been indicated. In any organic body whatever, if an atom of hydrogen united with carbon be replaced by a methyl group, CH 3 , the superior homologue of that body is obtained, that is, the compound which differs from the original body by the addition of CH 2 . There is a great resemblance in physical and chemical properties between such homologues. Some of these homologous series will be indicated farther on. Immediate Principles and Chemical Species. The four elements, carbon, hydrogen, oxygen, and nitrogen, are the more ordinary elements of organic compounds. Those which are found in nature in the organs of plants and animals, and which have been called by Chevreul immediate principles, contain no others, excepting sulphur, which exists in certain of them. 406 ELEMENTS OF MODERN CHEMISTRY. But nearly all of the other elements can be introduced artificially into organic compounds ; it is thus with bromine, iodine, phos- phorus, arsenic, boron, silicon, and a great number of the metals. In uniting with carbon, in different manners and in various proportions, these elements form an innumerable multitude of compounds, each of which has a fixed composition and definite properties. These bodies constitute the chemical species, so to say. When submitted to the action of reagents, all may be modified in a thousand manners, and transformed into each other. Sometimes their composition is simplified, one or more carbon atoms being removed from the chain. Sometimes it is complicated by the addition of new atoms of carbon. All of these bodies contain carbon, and are distinguished from each other : 1. By the number of carbon atoms contained in the molecule. 2. By the nature and arrangement of the other atoms com- bined with the carbon. 3. By the arrangement of all of the atoms in the molecule. The facts relative to the atomic composition of organic com- pounds are obtained by elementary analysis and by the deter- mination of the molecular weight. ELEMENTARY ANALYSIS. The object of elementary analysis is the determination of the nature and proportion of the elements contained in any given organic body. We can give here but a summary descrip- tion of the processes employed, considering only those which have for object the determination of carbon, hydrogen, and ni- trogen. These, together, with oxygen, are the more ordinary elements of organic combinations. In a substance containing carbon, hydrogen, and oxygen, the first two elements are determined directly in the same operation ; the oxygen is determined by difference. When, in addition to the former elements, the body contains nitrogen, the determination of this requires a separate operation. Determination of Carbon and Hydrogen. To determine the proportion of carbon and hydrogen contained in 100 parts of any given organic substance, the carbon is converted into car- bon dioxide, which is collected and weighed, and the hydrogen into water, which is condensed and weighed. These operations are conducted according to the processes indicated by Liebig. ELEMENTARY ANALYSIS. 407 For this end, the organic matter, previously dried with care, is burned with an excess of cupric oxide. The operation is exe- cuted in a combustion-tube of hard glass, which is wrapped with a spiral of metallic foil to prevent it from bending and swell- ing under the influence of the heat. Well-dried cupric oxide is introduced into the tube, then an intimate mixture of the substance to be analyzed with a large excess of the same oxide, and the remainder of the tube is filled with pure cupric oxide. The tube is then placed in a combustion furnace, and its open extremity is put in communication with (1) an U tube,^ (Fig. 120), containing fragments of calcium chloride in the first branch, and pumice-stone impregnated with sulphuric acid in the second; (2) a tube with five bulbs, h, called Liebig's potash bulbs, containing a concentrated solution of potassium hydrate, and followed by a small U tube, i, containing pumice-stone im- pregnated with potassium hydrate in the first branch, and frag- ments of potassium hydrate in the second. These different tubes have first been accurately weighed. When the appa- ratus is arranged, the combustion- tube is slowly heated, com- mencing at the extremity B, and gradually extending the heat so that each part of the tube is successively heated to redness. The water formed by the combustion is collected in the first U tube, the carbon dioxide is absorbed by the potassium hy- drate in the bulbs. When the operation is terminated, the drawn-out point of the combustion-tube is broken, and con- nected by means of a caoutchouc tube with a gasometer con- taining oxygen. An excess of the latter gas is then passed through the combustion-tube, in order to drive out the traces of carbon dioxide and aqueous vapor which it contains at the end of the combustion. It is then only necessary to weigh the water tube and the carbon dioxide tubes. The increase in weight which is found indicates, on one hand, the quantity of water, and on the other the quantity of carbon dioxide, pro- duced by the combustion of the organic matter. The compo- sition of water and of carbon dioxide being known, it is easy to deduce from the weight of these two bodies the quantities of hydrogen and carbon contained in the analyzed substance, and consequently the proportion of these two elements con- tained in 100 parts of that substance. Fig. 120 represents the operation towards its close : the combustion-tube is in the gas-furnace, B, and communicates, on the right with the tubes y, h, i, destined to receive the pro- 408 ELEMENTS OF MODERN CHEMISTRY. ELEMENTARY ANALYSIS. 409 ducts of the combustion, on the left with two large U tubes, the first of which is filled with pumice-stone impregnated with potassium hydrate to absorb traces of carbon dioxide, the second with pumice-stone saturated with sulphuric acid to absorb moisture. Through these tubes is passed the oxygen, at the close of the operation, to expel the last portions of carbon dioxide and vapor of water. When the substance contains carbon, hydrogen, and oxygen, the proportion of oxygen is the difference between the total percentage of carbon and hydrogen found and 100. . 121. Determination of Nitrogen, Nitrogen may be determined by two processes. The first consists in burning a given weight of the nitrogenized substance with an excess of cupric oxide. The carbon of the substance is converted into carbon dioxide ; the hydrogen is converted into water ; the nitrogen is disen- gaged. The gases, nitrogen and carbon dioxide, are received in a graduated jar standing on the mercury-trough and con- taining potassium hydrate. The carbon dioxide is absorbed, the nitrogen remains. At the close of the operation, the last traces of nitrogen are expelled by a current of carbon dioxide. The volume of nitrogen is then measured^ and its weight de- duced from its volume (Dumas). The second process (Fig. 121) consists in decomposing the nitrogenized organic matter with an alkali at a high tempera- s 35 410 ELEMENTS OF MODERN CHEMISTRY. ture. By this means all of the nitrogen is converted into ammonia. The substance is intimately mixed with soda lime, that is, lime impregnated with caustic soda. The mixture is heated to redness in a tube of hard glass, and the ammonia is received in a tube with three bulbs containing dilute hydro- chloric acid. Ammonium chloride is formed ; when the opera- tion is terminated, the liquid containing the salt is mixed with a solution of platinic chloride. It is then evaporated and exhausted with alcohol, which leaves the platinum and ammo- nium double chloride, 2(NH 4 C1) -f PtCl 4 . The latter is col- lected upon a tared filter, then washed and dried. From its weight is calculated that of the nitrogen contained in the organic substance (Will and Varrentrapp). The ammonia disengaged may also be received in 10 cubic centimetres of a normal solution of sulphuric acid, that is, an acid liquor containing a known quantity of sulphuric acid in a determined volume. The strength of this acid is determined by neutralizing 10 c.c. of it with a dilute alkaline solution of known strength and noting the volume of the latter required. The same operation is repeated with the 10 c.c. of which the acid has been par- tially neutralized by the ammonia. The quantity of ammonia corresponds to the difference between the volumes of the alka- line liquid employed in these two operations, and can easily be calculated by simple proportion (Peligot). Determination of the Molecular Weight of Organic Sub- stances. Elementary analysis permits the determination of the centesimal composition of organic substances. This is indispensable, but it is insufficient for the establishment of their atomic composition, that is, the number of atoms of car- bon, hydrogen, oxygen, and nitrogen which are contained in a single molecule of a given organic compound. But if the weight of the molecule be known (hydrogen being taken as unity), it is easy to deduce the atomic composition from the figures given by elementary analysis, as will be seen by the following example. By elementary analysis it is found that 100 parts of acetic acid contain Carbon 40. Hydrogen 6.67 Oxygen . 53.33 100JOO On the other hand, methods which will be described have ELEMENTARY ANALYSIS. 411 shown that the molecular weight of acetic acid is 60 ; that is to say, the total weight of the atoms of carbon, hydrogen, and oxygen contained in a molecule of acetic acid, is 60. Hence by the following proportions : If 100 parts acetic acid contain 40 of carbon, 60 parts contain x. " " " 6.67 of hydrogen, " " y. " " 53.33 of oxygen " " z. From which, x = 24 ; y = 4 ; z = 32. Hence 24 represents the weight of the atoms of C contained in a molecule of acetic acid. 4 represents the weight of the atoms of H contained in a molecule of acetic acid. 32 represents the weight of the atoms of contained in a molecule of acetic acid. By dividing these numbers by the weights of the respective atoms, the number of atoms of C, H, and O contained in a molecule of acetic acid is readily determined. 24 -s- 12 = 2 atoms of carbon. 4-s-l=4 " hydrogen. 32-5-16 = 2 " oxygen. Hence the formula of acetic acid is C 2 H*0*. After the analysis of an organic substance has been made, it is only necessary to determine its molecular weight in order to establish its atomic composition. Several processes are em- ployed for this determination, of which the most sure is the determination of the vapor density. We know that if one atom of hydrogen occupy one volume, the molecules of organic substances occupy two volumes. To find the weights of these molecules it is then sufficient to deter- mine their vapor densities compared to hydrogen ; that is, to find the weight of one volume of their vapors, that of one volume of H being taken as unity. The number found mul- tiplied by 2 gives the weight of two volumes, that is, the weight of the molecule. Hence a simple determination of the vapor density is suf- ficient for the establishment of the molecular weight. Ordi- narily these vapor densities are given as compared with air taken as unity. To bring them to the hydrogen scale it is then only necessary to multiply them by 14.44, which is the exact relation of the density of air to that of hydrogen. Thus the vapor density of acetic acid, determined at 295, has been found equal to 2.083 (Cahours). This number multiplied by 14.44 gives for the density compared to hydrogen 30.08. The 412 ELEMENTS OF MODERN CHEMISTRY. latter number expresses the weight of one volume of acetic acid vapor, the weight of one volume of hydrogen being con- sidered as 1. The weight of two volumes of this vapor, that is, the weight of the molecule, will then be 2 X 30.08 60.16, a number very nearly approaching 60, the theoretical molecular weight. The method just described can only be applied to substances which can be volatilized without decomposition. For other bodies another method must be adopted. The latter consists in forming with the organic body definite combinations, the atomic composition of which may be known. We will again consider acetic acid. Salts may be formed with this acid, and we know that these salts contain one atom of metal. We may then analyze silver acetate. 100 parts of that salt contain 64.67 parts of silver. This fact being known, it is easy to deter- mine the molecular weight of silver acetate. Since the latter contains one atom of silver, we can conclude, if 64.67 parts of silver are contained in 100 parts of silver acetate, 108 parts of silver, that is, one atom, are contained in x parts of silver acetate ; whence x = 167. This number represents the molec- ular weight of silver acetate. That of acetic acid may be de- duced by substituting the atomic weight of hydrogen for that of silver, which gives for the molecular weight of acetic acid 60. Analogous operations and reasoning permit the determina- tion of the molecular weights of bodies playing the part of bases. They are combined with an acid, the molecular weight of which is known, and the composition of- the combination furnishes the data for the calculation of the molecular weight of the base. This method can be applied in a large number of analogous cases, and presents a great generality. ISOMERISM, METAMERISM, POLYMERISM. Elementary analysis demonstrates that many bodies which differ in their physical and chemical proparties, possess exactly the same centesimal composition. Such bodies are said to be isomeric. Two kinds of isomerism exist. Sometimes the isomeric bodies contain the same number of similar atoms in molecules of the same size, and differ only by the arrange- ment of these atoms ; sometimes they contain similar atoms united in the same proportion, but not in the same number, in molecules of unequal magnitude. ISOMERISM, METAMERISM, POLYMERISM. 413 In both cases the centesimal composition is the same, for it depends only on the relative number of the atoms. The first kind of isomerism constitutes metamerism; the second, polymerism. Acetic acid and methyl formate are an example of two metameric bodies. Each contains 2 atoms of carbon, 4 of hydrogen, and 2 of oxygen ; their molecules are equal in size, but diiferent in atomic structure. The latter fact may be expressed by the following formulae : C 2 H 3 O.OH acetic acid CH 3 O.OCH methyl formate The first expresses that acetic acid contains a group of atoms, C 2 H 3 0, acetyl, which is united with hydroxyl, OH ; the second, that methyl formate contains a group, CHO, formyl, which is united with oxymethyl, CH 3 0. The difference in the atomic arrangement becomes evident, if the preceding formulae be developed in the graphic manner. 0-H O-CH 3 I I I I CH 3 H Acetic acid. Methyl formate. By adopting the theory of atomicity, chemists have been enabled to discover the atomic structure of a great number of combinations, as we have seen in the case of acetic acid and methyl formate. Such considerations are of great importance for the interpretation of isomerism, and we will have frequent occasion to refer to the subject in the course of this work. Acetic acid and glucose or grape-sugar present an example of polymerism. Both contain the atoms of carbon, hydrogen, and oxygen, united together in the same proportions, but the molecule of the second contains three times as many of each as that of the first. C 2 H*0 2 acetic acid. 3 X C*HK) 2 = CH 12 6 glucose. Among the more important and better known cases of po- lymerism, may be mentioned the numerous hydrocarbons which present the centesimal composition of ethylene or olefiant gas, and which diifer from it by the regularly increasing number of their atoms of carbon and hydrogen. These bodies form the following homologous series : 35* 414 ELEMENTS OF MODERN CHEMISTRY. C 2 H* ethylene. C 3 H 6 propylene. C 4 H 8 butylene. C 5 H 10 amylene. C 6 RU hexylene. C?H" heptylene. C 8 Hi octylene, etc. It will be seen that butylene contains twice as many carbon and hydrogen atoms as ethylene, hexylene contains three times as many, etc. FUNCTIONS OF OKGANIC COMPOUNDS. In the study of mineral chemistry it has been seen that bodies present great differences in properties, according to their composition. Some are simple and apt to enter into combina- tion ; others are compound and indifferent ; the first are more or less energetic in their affinities, the others saturated and satisfied. In one case, we have examined either more or less powerful acids or bases, some of which are hydrated, as potassa and soda, others anhydrous, as the oxides of lead and silver. In the other case, we have studied the salts resulting from the union of the former bodies. In organic chemistry we again encounter various kinds of bodies which have different functions, according to their com- position. It may be said, in a general manner, that the properties of compound bodies depend upon the nature of the atoms and their arrangement in the molecule. In treating of isomerism, the influence of the latter condition has been indicated ; that of the former is still more powerful. Water and potassium hydrate are both constituted, and in an analogous manner, of three elementary atoms. Each con- tains one atom of oxygen united to two monatomic atoms. HOH KOH Water. Potassium hydrate. But what a difference in their properties ! But may not this be expected when it is considered that one contains the energetic metal potassium, in the place occupied in the other by the light gas hydrogen ? Is the difference between potassa and water greater than that between potassium and hydrogen ? MON ATOMIC COMPOUNDS. 415 And if for the two atoms of hydrogen we substitute two atoms of chlorine, is it not to be expected that hypochlorous oxide C1-0-C1 the molecule of which is similar in structure to that of water, shall differ from the latter in its properties as much as chlo- rine differs from hydrogen ? It is thus that the nature of the elements contained in compound bodies is the dominant condi- tion in the manifestation of their properties. The following considerations are of a nature to demonstrate the truth of this proposition inasmuch as concerns organic compounds : MONATOMIC COMPOUNDS. Saturated Hydrocarbons. The hydrocarbons belonging to the series of marsh gas are all saturated. Consider, for example, C 2 H 6 ; all of the atomicities of two atoms of carbon are satisfied by the union of the latter together and with six atoms of hydrogen. HH H-C-C-H i i H H Ethane, or ethyl hydride. It is the same with all of its homologues ; the hydrides of propyl, butyl, amyl, etc., are all saturated hydrocarbons, as will be seen by developing the formula of any one of them, pentane, for example : HHHHH i I I I i H-C-C-C-C-C-H i i i i i HHHHH Pentane, or amyl hydride. All of these bodies are incapable of fixing other elements by direct addition, but they may be modified by substitution, that is, one or several of their atoms of hydrogen may be replaced by other elements. Mpnatomic Chlorides, Bromides, and Iodides. By the reaction of bromine upon any of the hydrocarbons, we may 416 ELEMENTS OF MODERN CHEMISTRY. obtain compounds containing an atom of bromine in the place of an atom of hydrogen. C 2 H 6 -f Br 2 = C 2 H 5 Br -f- HBr Ethane. Ethyl bromide. A saturated and indifferent hydrocarbon is thus converted into a bromide. The corresponding chloride and iodide exist, possessing the same constitution as the primitive hydrocarbon, and forming with it the following series : C 2 H 6 ethane. C 2 H&C1 ethyl chloride. C 2 H5Br ethyl bromide. CH5I ethyl iodide. To the other hydrocarbons correspond chlorides, bromides, and iodides analogous to the preceding. Thus, the following groups are known : CH* methane. C 5 H 12 pentane. CH 3 C1 methyl chloride. C 5 H n Cl amyl chloride. CH 3 Br methyl bromide. C 5 HUBr amyl bromide. CH 3 I methyl iodide. C 5 H U I amyl iodide. All of these bodies may be made to undergo the most varied transformations. They may be attacked by a number of re- agents, to which they present a hold, as it were, since the chlo- rine, bromine, and iodine which they contain are gifted with powerful affinities. The residues resulting from the subtraction of the chlorine, bromine, or iodine then enter into other combinations. It will be remarked that these residues represent the saturated hydro- carbons from which one atom of hydrogen has been removed. CH 3 =CH 3 Br Br, orCH 4 H = c 2 H 5 Br Br, or C 2 H 6 H 11 = C 5 H n Br Br, or C 5 H 12 H The atoms of carbon contained in these residues, CH 3 , C 2 H 5 , and C 5 H n , are no longer entirely saturated, since Cl, Br, I, or H has been removed, elements which saturated one atomicity. Therefore, these residues are capable of entering other com- binations, but as they possess only one free atomicity, they can only saturate one when they combine. This is expressed by saying that they play the part of monatomic radicals. The chlorides, bromides, and iodides from which they are derived are themselves monatomic. MONATOMIC COMPOUNDS. 41t Alcohols. The neutral organic hydrates corresponding to the preceding chlorides, bromides, and iodides, are called alcohols. If ethyl iodide be heated for a sufficiently long time with potassium hydrate, potassium iodide will be formed, and the alkaline liquid will contain alcohol which may be separated. This body is ethyl hydrate and is formed according to the following reaction : Cm 5 ! + KOH = KI + C 2 H 5 .OH Ethyl iodide. Ethyl hydrate. It is formed, as is seen, by double decomposition. The potassium having removed the iodine from the ethyl iodide, the monatomic residue C 2 H 5 combines with the monatomic residue OH. Alcohol is then the hydrate which corresponds to the iodide, C 2 H 5 I, and to the hydrocarbon, C 2 H 6 . Analo- gous hydrates correspond to the other hydrocarbons of the same series ; they constitute the series of monatomic alcohols, and may be denned as derived from the saturated hydrocarbons by the substitution of the group hydroxyl for one atom of hydrogen. The alcohols now known are numerous ; the follow- ing are some of them: CIROII methyl hydrate, or methylic alcohol. C*H 5 .OH ethyl hydrate, or ethylic alcohol. C 3 H 7 .OH propyl hydrate, or propylic alcohol. C*H 9 .OH butyl hydrate, or butylic alcohol. C 5 H U .OH amyl hydrate, or amylic alcohol. C 6 H 13 .OH hexyl hydrate, or hexylic alcohol. C 7 H 15 .OH heptyl hydrate, or heptylic alcohol. C 8 H 17 .OH octyl hydrate, or octylic alcohol. Each member of this series differs from that which follows by CH 2 . All are allied by analogous properties. These two conditions characterize homologous bodies. The alcohols of which the general formula is C n H 2n+1 OH, form one of the most important series of homologues. If one of these alcohols be heated with hydrochloric, hydro- bromic, or hydriodic acid, water will be formed and the alcohol will be converted into a monatomic chloride, bromide, or iodide. In this reaction the hydroxyl, OH, is replaced by chlorine, bromine, or iodine. C 2 H 5 .OH + HC1 = H 2 + C 2 H 5 C1 Ethyl hydrate. Ethyl chloride. The bodies thus formed are the monatomic chlorides, bro- 8* 418 ELEMENTS OP MODERN CHEMISTRY. mides, or iodides before considered. These experiments expose the relations which exist between the latter compounds and the corresponding hydrates, which are the alcohols. Monobasic Acids. Acetic acid, which exists in vinegar, is a derivative of alcohol, of which it is one of the products of oxidation. It is formed under many conditions, one of which is the oxidation of alcohol vapor on contact with platinum black and the air. C 2 H 5 .OH -+ O 3 = C 2 H 3 O.OH + H 2 Alcohol. Acetic acid. In this reaction an atom of oxygen removes two atoms of hydrogen to form water, and the place of these two atoms of hydrogen is filled by another atom of oxygen. The group ethyl, C 2 H 5 , thus becomes the group acetyl, C 2 H 3 0, and if alcohol be the hydrate of ethyl, acetic acid is the hydrate of acetyl. We can account for this reaction by developing the formulae of alcohol and acetic acid according to the principles before explained. HH HO H-C-C-OH -f = H-C-C-OH -f H 2 O i I i HH H Alcohol. Acetic acid. In alcohol, the second carbon atom is combined with two atoms of hydrogen and with one group hydroxyl, while in acetic acid it is combined with an atom of oxygen and a group hydroxyl. Acetic acid contains two atoms of carbon united together, and combined, the one with H 3 , the second with and OH. It is thus formed of a group CH 3 united to a group CO-OH = C0 2 H. There exist many other acids analogous to acetic acid, and derived, like it, by oxidation of the monatomic alco- hols of the series C n H 2n+1 OH. All of these acids contain a hydrocarbon group analogous to methyl, combined with the group C0 2 H = CO-OH. The hydrogen of the latter group can be readily replaced by an equivalent quantity of metal. This hydrogen is said to be strongly basic, and all of the organic acids which contain a single group, C0 2 H, united to a hydro- carbon group, are monobasic like acetic acid. The homologues of the latter form the following series : MONATOMIC COMPOUNDS. 419 C H2 02 == H -CQ2H formic acid. C2 H* O 2 = C H 3 -C0 2 H acetic acid. C 3 H 6 O 2 == C 2 H 5 -C0 2 H propionic acid. C* H 8 O 2 = C 3 U 7 -C0 2 H butyric acid. C 5 HK>0 2 = C 4 H -C0 2 H valeric acid. C 6 H 12 2 = C 5 H 11 -C0 2 H caproic acid. C 7 H"0 2 = C 6 H 13 -C0 2 H oenanthic acid. C 8 H 16 2 = C 7 H 15 -C0 2 H caprylic acid. C 9 H 18 2 = C 8 H 17 -C0 2 H pelargonic acid. CiOflMQ 2 = CHi-C0 2 H capric acid, etc. The first series of formulae indicates simply the nature and number of atoms contained in the acids of the series C n H 2n 2 . They are empirical formulae. The second series gives certain indications upon the relations existing between these atoms. They are rational formulae, and when developed so as to ex- press the relations between all of the atoms, they become constitutional formulae. Compound Ethers. The compound ethers are combina- tions which represent acids of which the hydrogen has been replaced by an alcoholic group. If one of the alcohols of the preceding series, ordinary alco- hol, for example, be heated for a long time with acetic acid, water will be formed, and a volatile, neutral liquid possessing an agreeable odor may be separated from the product ; this sub- stance is ethyl acetate, or acetic ether. It is formed according to the following reaction : C 2 H 5 .OH + C 2 H 3 O.OH = C 2 H 5 0(C 2 H 3 0) + H 2 Alcohol. Acetic acid. Ethyl acetate. On comparing this compound with alcohol, we find that it is formed by substitution of the group C 2 H 3 0, the existence of which is admitted in acetic acid, and which is called acetyl, for one atom of hydrogen in alcohol ; and this atom of hydro- gen which is replaceable by acetyl is that which is united to the oxygen in alcohol, that which forms a part of the hydroxyl group. The other atoms of hydrogen, those which constitute part of the group C 2 H 5 , cannot be replaced by acetyl. All of the acids can form with alcohol, and indeed with all of the alcohols, compounds analogous to ethyl acetate, and these combinations are called compound ethers. The property possessed by the alcohols of etherifying acids is general and characteristic of this class of compounds. Alcohols which require for etherification but a single molecule of an acid anal- 420 ELEMENTS OF MODERN CHEMISTRY. ogous to acetic acid are called monatomic. Many exist which are not included in the preceding series. Aldehydes, Acetic acid is not the only product of the oxidation of alcohol. There is another compound interme- diate between these two ; it results from the action of a single atom of oxygen upon the molecule of alcohol, which thus loses two atoms of hydrogen without other change. The new com- pound is aldehyde. C 2 H 6 + = H 2 -f C 2 H 4 Alcohol. Aldehyde. It is a very volatile liquid having a great tendency to become oxidized and converted into acetic acid. It forms crystalline combinations with the alkaline acid-sulphites. To the other alcohols of the series C n H 2n+2 O, and other acids of the series C n H 2n 2 , correspond compounds analogous to aldehyde by their composition and by their properties. They form the following series: C 2 H 4 aldehyde or acetaldehyde. C 3 H 6 propionic aldehyde. C*H 8 butyric aldehyde. valeric aldehyde, etc. Acetones. When calcium acetate is submitted to dry distil- lation a neutral, volatile liquid is obtained, having a peculiar aromatic odor, and known by the name acetone. Ca "ic 2 iro 2 = C3H6 + CaC 3 Calcium acetate. Acetone. Calcium carbonate. To the other acids of the acetic acid series correspond bodies analogous to acetone, and forming with it a homologous series. These acetones are related by properties and composition to the aldehydes. Like the latter, they form crystalline combinations with the alkaline acid-sulphites. It may be considered that while aldehyde is the hydride of acetyl, acetone is the methyl- ide of acetyl, and that in general the acetones are derived by the substitution of an alcoholic group, analogous to methyl, for an atom of hydrogen in the aldehydes considered as hydrides. CH 3 -CO-H CH 3 -CO-CH 3 Aldehyde (acetyl hydride). Acetone (acetyl methylide). Hence, acetone contains two methyl groups united to a group, CO (carbonyl). Its mode of formation justifies this conclusion, MONATOMIC COMPOUNDS. 421 as shown in the following equation, in which the constitutional formula of acetic acid is employed : CH'IcOO >Ca = Ca " C 3 + CH 3 -CO-CH* Calcium acetate. Calcium carbonate. Acetone. Chlorides of Acid Radicals. In the preceding compounds we have admitted the existence of a group, C 2 H 3 = CH 3 -CO, existing in combination with OH in acetic acid, C 2 H 3 O.OH, with hydrogen in aldehyde, C 2 H 3 O.H, and with methyl in ace- tone, C 2 H 3 O.CH 3 . A compound is known in which this same group is united with chlorine. Acetyl chloride, C 2 H 3 O.C1, is a monatomic chloride, like ethyl chloride, C 2 H 5 C1, from which it is distinguished by the strongly electro-negative nature of its radical. If acetyl chloride be poured into water, it disappears in a short time with development of heat and the formation of acetic and hydrochloric acids. C 2 H 3 O.C1 + H 2 = CTFO.OH + HC1 Acetyl chloride. Acetic acid. To acetyl chloride correspond other chlorides which contain radicals of acids analogous to acetic acid. When they are treated with water they yield hydrochloric acid and the acids corresponding to their radicals. C 3 H 5 O.C1 C 3 H 5 O.OH Propionyl chloride. Propionic acid. C 4 H 7 O.C1 C 4 H 7 O.OH Butyryl chloride. Butyric acid. C 7 H 5 O.C1 C 7 H 5 O.OH Benzoyl chloride. Benzoic acid. Amides. If acetyl chloride be treated with ammonia, am- monium chloride will be formed, together with a solid, neutral, nitrogenized body called acetamide. C 2 H 5 O.C1 + 2NH 3 = NH 4 C1 + C 2 H 3 O.NH 2 Acetyl chloride. Acetamide. There are many other compounds similar to acetamide, and known by the name amides. They are formed by the action of ammonia upon organic chlorides analogous to acetyl chloride. They are also formed by the action of heat upon the ammo- niacal salts of the monobasic acids. The latter compounds then lose one molecule of water, and are converted into amides. C 5 H 9 O.ONH 4 = C 5 H 9 O.NH 2 + H 2 Ammonium valerate. Valeramide. 36 422 ELEMENTS OF MODERN CHEMISTRY. Acetamide may be regarded as ammonia in which an atom of hydrogen has been replaced by the radical acetyl. ( H ( C 2 H 3 f C 5 H 9 NfH N^H N^H (H (H (H Ammonia. Acetamide. Valeramide. Compound Ammonias, or Amines. If ethyl iodide be heated with ammonia, one of the products of the reaction will be the hydriodide of a base derived from ammonia by the sub- stitution of an ethyl group for an atom of hydrogen. C 2 H 5 I + NH 3 = (C 2 H 5 )NH 2 .HI Ethyl iodide. Ethylamine hydriodide. In this reaction, other ethylated bases are formed, independ- ently of ethylamine, among which must be mentioned diethyl- amine and triethylamine. All present the most striking anal- ogy to ammonia. They may be regarded as ammonia in which one, two, or three atoms of hydrogen have been replaced by one, two, or three ethyl groups. H) C 2 H 5 ) C 2 H 5 ) C 2 H 5 ) H V- N H t N C 2 H 5 I N C 2 H 5 ( N H \ H ) H ) C 2 H 5 ) Ammonia. Ethylamine. Diethylamine. Triethylamine. The other alcoholic groups, C n H 2n+1 , can in the same man- ner replace one or more atoms of hydrogen in ammonia. The results are bases having constitutions analogous to those of the ethyl bases. They are called amines, or compound ammonias. It is necessary that the signification of the formulae above given and those that are to follow shall be clearly understood. They are examples of typical notation, and indicate the rela- tions of the compounds with the type ammonia. (H N'" 1 H (H The brace joining the three hydrogen atoms signifies that the whole three are united to a single atom of triatomic nitro- gen, with which each exchanges one atomicity; this may be expressed by writing the formula for ammonia thus : MONATOMIC COMPOUNDS. 423 What, then, takes place when one or more atoms of hydro- gen are replaced by a group like ethyl ? The latter exchanges one atomicity with the nitrogen atom, precisely as the hydro- gen atom did, and combines with the nitrogen by one of the atoms of carbon of the group ethyl, CH 3 -CH 2 , which requires the satisfaction of one atomicity. This is clearly expressed in the following graphic formulae : H H N-CH 2 -CH 3 N-CH 2 -CH 3 H ilP-CH 3 Ethylamine. Diethylamine. However, such formulae would be too cumbrous for ordinary use, and our formulae must be more condensed. /WW /C 2 H 5 N^H N^C 2 H 5 N(C 2 H 5 ) 3 X H X H Ethylamine. Diethylamine. Triethylamine. Phosphines. Arsines. Stibines. There exist several se- ries of combinations belonging to the same type as the com- pound ammonias, but in which the nitrogen is replaced by phosphorus, arsenic, or antimony. These compounds are de- rived from the hydrogen compounds of phosphorus, arsenic, and antimony by the substitution of one or more alcoholic groups for one or more atoms of hydrogen. H } P C 2 H 5 V P C 2 H 5 H ) H ) C 2 H 5 Hydrogen phosphide. Ethylphosphine. Diethylphosphine. Trieth.vlphosphine. H) CH 3 ) CH) CH 3 ) HUs H ( As CH^As CH 3 Us HJ H) CTJ CH 3 ) Hydrogen arsenide. Methylarsine. Dimethylarsine Trimethylarsine. TT -x chloride. H H [ Sb C 2 H 5 \ Sb H ) C 2 H 5 ) Hydrogen antimonide. Triethylstibine. Organo-metallic Compounds. Ethyl and its congeneric compounds, methyl, amyl, etc., can enter into combination not only with nitrogen, phosphorus, arsenic, etc., of which they saturate one or more atomicities, but with a large number of 424 ELEMENTS OF MODERN CHEMISTRY. metals. Thus, zinc, which is diatomic, can combine with two ethyl groups to form zinc ethyl. 7 (C 2 H 5 /n { C 2 H 5 Mercury, also diatomic, can unite with one or two ethyl or methyl groups, etc. In the second case, the new combination is saturated ; in the first, it is monatomic, (Hg"C 2 H 5 /, and re- quires for saturation an atom of a monatomic element, or a monatomic group, iodine, for example. TT Cyanic acid. Ethylamine. Ethylurea. CON(C 2 H 5 ) + NH 3 = Ethyl cyanate. Ethylurea. The following is the nomenclature and composition of some of the principal compound ureas : CH*N 2 urea. CH 3 (CH 3 )N 2 methylurea. CH*(CH5)N*0 ethylurea. CH 2 (C 2 H5) 2 N 2 diethylurea. CH(C 2 H5) 3 N 2 triethylurea. CH 3 (C5HU)N 2 araylurea. CH 3 (C 6 I15)N 2 phenylurea. CH 2 (C 6 H 5 ) 2 S*0 diphenylurca. 444 ELEMENTS OF MODERN CHEMISTRY. POTASSIUM SULPHOCYANATE. KCSN This salt, which is sometimes called potassium sulphocyanide, corresponds to the cyanate, in which the oxygen is replaced by sulphur. It is prepared by heating a mixture of two parts of potas- sium ferrocyanide and one part of sublimed sulphur to redness in a crucible or luted matrass. After cooling, the mass is dissolved in water, the solution filtered, and potassium carbon- ate added to the liquor as long as a precipitate of ferrous car- bonate is formed. The solution is again filtered, evaporated to dryness, the residue exhausted with alcohol, and the alcoholic solution allowed to evaporate spontaneously. Potassium sulphocyanate crystallizes in long striated prisms resembling potassium nitrate, or in needles terminated by four- faced points. It is deliquescent and very soluble in water and alcohol. Solution of potassium sulphocyanate produces an intense blood-red color with the ferric salts, due to the formation of ferric sulphocyanate. Ammonium Sulphocyanate, NH 4 CSN. This body corre- sponds to ammonium cyanate. It occurs in the water from the purification of coal-gas. When heated to 170 , it is converted NTT 2 into sulpho-urea, CS0 Methane, or methyl hydride. Methyl hydrate. f1TT3 CH 3 C1 Methyl chloride. Methyl oxide. CHCP 2 CIP> Chloroform. Methyl acetate. These compounds will be but briefly described. METHANE. (MARSH GAS.) CH* The inflammable gas which is disengaged from the mud of marshes is impure methane. The same gas is frequently evolved in the galleries of coal mines, and constitutes the fire-damp of miners. It is produced artificially by the action of an excess of alkali upon acetic acid (Persoz, Dumas). Preparation. Methane is most conveniently prepared in the pure state by strongly heating in a glass flask or retort a mixture of 1 part of sodium acetate, 1 part of potassium hy- drate, and 1 parts of lime ; the lime is added to prevent the action of the potassium hydrate upon the glass. The gas may be collected over water. NaC 2 H 3 2 + NaOH = CH 4 + Na 2 C0 3 Sodium acetate. Methane. Properties. Methane is a colorless, odorless gas. Its den- 38 446 ELEMENTS OF MODERN CHEMISTRY. sity is 0.559 ; it is but slightly soluble in water, somewhat more so in alcohol. It burns in the air with a yellow flame less lumi- nous than that of ethylene, or olefiant gas. A mixture of me- thane and oxygen explodes violently on the application of flame or the passage of an electric spark. If two volumes of methane and four volumes of oxygen be introduced into an eudiometer and the spark be passed, a bright flash is visible. After the combustion, the mercury rises in the tube, and it is found that the volume of gas is reduced to one- third of the primitive volume (to 2 volumes) ; if a solution of potassium hydrate be introduced, the whole of the remaining gas will be absorbed. 2 volumes of methane produce in burning 2 volumes of carbon dioxide, and require 4 volumes of oxygen. This experiment permits the determination of the composition of methane. 2 volumes of carbon dioxide contain 2 volumes of oxygen combined with 1 volume (1 atom) of carbon ; consequently two volumes of marsh gas contain one atom of carbon. The other two volumes of oxygen consumed have combined with four volumes of hydrogen, which are likewise contained in two volumes of methane. Consequently two volumes of methane contain 1 atom of carbon and 4 atoms of hydrogen. A mixture of chlorine and methane explodes when exposed to direct sunlight. In diffused daylight, the action is less violent, especially if an inert gas, such as carbon dioxide, be added. In this case, methyl chloride is formed, and in presence of an excess of chlorine, chloroform, and finally carbon tetrachloride. CH 4 + GT =* HC1 -f CH 3 C1 methyl chloride. CH 4 + 3C1 2 = 3HC1 -f CHCP chloroform. CH 4 + 4CP = 4HC1 -f CC1 4 carbon tetrachloride. It is seen that in these reactions the chlorine is substituted for hydrogen, atom for atom. Inversely, when chloroform or carbon tetrachloride is sub- mitted to the action of nascent hydrogen, an inverse substitu- tion may be effected, and these chlorine compounds may be converted into methane. This may be accomplished by putting them in contact with sodium amalgam and water. The latter is decomposed by the sodium, and constitutes a source of hy- drogen (Melsens). CHOP + 3H 2 = 3HC1 -f CH* METHYL HYDRATE METHYL OXIDE. 44*7 METHYL HYDRATE, OR METHYL ALCOHOL. (WOOD-SPIRIT.) CHK) = CH3-OH The products of the dry distillation of wood contain about one per cent, of a spirituous liquid, which was discovered in 1812 by Taylor, and named wood-spirit. It is separated by several distillations and rectifications over lime ; for, being more volatile than the other products, it passes over first. When pure, it is a mobile, colorless liquid, having an alco- holic odor. It boils at 66.5. Its density at is 0.8142 (Dumas and PeligotJ. It is inflammable and burns with an almost colorless flame. It is miscible with water, alcohol, and ether in all proportions. It dissolves caustic baryta and forms with it a definite combi- nation. It forms a crystalline compound with calcium chloride containing CaCP -f 4CH 4 0. Potassium and sodium react energetically upon methyl hy- drate ; the metal dissolves with disengagement of hydrogen and formation of potassium or sodium methylate. CH 3 -OH CH 3 -OK Methyl hydrate. Potassium metbylate. If methyl alcohol be placed under a bell-jar containing also some watch-glasses filled with platinum black, so that the vapor of the wood-spirit mixed with air may come in contact with the finely-divided metal, it is found that the liquid aoon becomes strongly acid. By the slow oxidation of the wood-spirit under these conditions, formic acid is produced (Dumas and Peligot). CH 3 -OH -f O 2 = CHO-OH -f H 2 Methyl hydrate. Formic acid. METHYL OXIDE. (CH 8 ) 2 O When methyl alcohol is heated with twice its weight of concentrated sulphuric acid, a colorless gas is disengaged, which is methyl oxide. 2CH 3 .OH = (CH 3 ) 2 + H 2 Methyl hydrate. Methyl oxide. 448 ELEMENTS OF MODERN CHEMISTRY. This gas is formed by the dehydration of methyl alcohol and the linking together of two methyl groups by an atom of oxygen. It is methylic ether. It holds the same relation to methyl hydrate that ordinary ether does to ethyl hydrate. It is colorless, very soluble in alcohol and ether, and quite soluble in water. It liquefies at a very low temperature (36). CHLORIDE, BROMIDE, AND IODIDE OF METHYL. These compounds may be regarded as marsh gas in which one atom of hydrogen is replaced by an atom of chlorine, bro- mine, or iodine. They are formed by the action of hydrochloric, hydrobromic, and hydriodic acids upon methyl alcohol. CH'.OH + HC1 = CH 3 C1 + H 2 They may be considered as derived from the hydracids by the substitution of the group methyl for the atom of hydrogen, HC1 (CH 3 )C1 Hydrochloric acid. Methyl chloride. Methyl chloride is a colorless gas, having an agreeable odor. When exposed to intense cold, it condenses to a liquid which boils at 22. When heated for a considerable time with a concentrated solution of potassium hydrate, it is converted into methyl alcohol. Methyl bromide, CH 3 Br, is a colorless liquid, boiling at 13. Methyl iodide, CH 3 I, boils at 43 ; its density at is 2.1992. It is made by gradually adding iodine to a mixture of methyl alcohol and amorphous phosphorus, and distilling. The dis- tilled liquid is mixed with water, which precipitates the iodide ; the dense liquid is separated, dried with calcium chloride, and distilled. CHLOROFORM. CHOP This important substance was discovered in 1831 by Soubei- ran and Liebig. It is made by distilling either alcohol or wood- spirit with a mixture of chloride of lime and calcium hydrate. The distilled liquid separates in two layers, of which the lower METHYL CYANIDE. 449 is impure chloroform. It is separated, washed first with water and then with a solution of potassium carbonate, and rectified over calcium chloride. Chloroform is a colorless, -very mobile liquid, having an agreeable, ethereal odor. Its density is 1.48, and it boils at 60.8. It does not take fire on contact with flame. It is but slightly soluble in water, but dissolves readily in alcohol and ether. It dissolves sulphur, phosphorus, fats, resins, a great number of the alkaloids, and in general, organic matters rich in carbon. By the prolonged action of chlorine, it is converted into carbon tetrachloride, CC1 4 , a colorless liquid boiling at 77. A boiling alcoholic solution of potassium hydrate converts it into formate and chloride. CHOP + 4KOH = 2H 2 + 3KC1 -f KCHO 2 Chloroform. 1'otassiuni formate. When chloroform is boiled with an alcoholic solution of ethylate of sodium, sodium chloride is formed, together with an ethereal compound, CH(OC 2 H 5 ) 3 , in which 3 ox ethyl groups, OC 2 H 5 , replace the 3 chlorine atoms of chloroform (Kay). CHOP -f 3NaO.C 2 H 5 = 3NaCl -f CH(OC 2 H 5 ) 3 Chloroform. Sodium ethylate. Kay's ether. Chloroform, heated to 180 with aqueous or alcoholic ammo- nia, yields ammonium cyanide and sal-ammoniac. This re- action takes place at 100, in presence of potassium hydrate. CHC1 3 + 5NH 3 = NH'CN + 3NH*C1 Chloroform acts in a remarkable manner upon the phenols in presence of an alkali such as soda or potassa, forming aro- matic aldehydes. This reaction, discovered by Reimer, will be described farther on (see Phenol). Chloroform is much employed in surgery as an anaesthetic. The inhalation of its vapor produces insensibility and loss of muscular action. METHYL CYANIDE. C 2 H 3 N =CH 3 Cy This body may be obtained by distilling a mixture of potas- sium methylsulphate and potassium cyanide, or by distilling acetamide with phosphoric anhydride, which removes one mol- ecule of water from the former body. 38* 450 ELEMENTS OF MODERN CHEMISTRY. C 2 H 3 O.NH 2 H 2 = C 2 H 3 N Acetanride. Methyl cyanide, or acetonJtrilp. The product obtained in the latter operation is called acc- tonitrile. Methyl cyanide is a colorless liquid, having a disagreeable odor ; it boils at 77. A boiling solution of potassium hydrate decomposes it into ammonia and potassium acetate. CH 3 -CN -f 2H 2 = CH 3 -CO.OH -f NH 3 Methyl cyanide. Acetic acid. Gautier has discovered an isomeride of methyl cyanide, methyl carbylamine. This body is formed, together with methyl cyanide, when a mixture of potassium methylsulphate and potassium cyanide is distilled. Under the influence of alka- lies, it decomposes into formic acid and methylamine. C s } N -f KOH + H 2 == KCHO 2 + C ^ j N Methyl carbylamine. Potassium formate. Methylamine. METHYL NITRATE. CH 3 .NO 3 This substance, which represents nitric acid in which the basic hydrogen is replaced by methyl, is an example of a com- pound methyl ether. It is prepared by introducing into a retort 50 grammes of powdered potassium nitrate, and adding a mixture of 100 grammes of sulphuric acid and 50 grammes of wood-spirit. The reaction begins in the cold, but must be finished by dis- tilling on a water-bath. The liquid condensed in the receiver is washed with water, and rectified several times over a mix- ture of massicot and calcium chloride. It is a colorless, neutral liquid ; density, 1.182 ; boiling-point, 66. Its vapor explodes violently when heated above 150. Methyl nitrate dissolves in ammonia, producing ammonium nitrate and methylamine. CH 3 .N0 3 -f 2NH 3 = NH 4 .N0 3 + CH 3 (NH 2 ) METHYL NITRITE AND NITROMETHANE. These two compounds present a remarkable instance of isomerism in very simple combinations. The first, CH 3 O.NO, which represents nitrous acid, HNO 2 , METHYL NITRITE AND NITROMETHANE. 451 in which the hydrogen is replaced by methyl, is obtained when methyl alcohol is heated with nitric acid in presence of copper. It is a liquid boiling at about 12. The second, called also nitrocarbol, represents methane, in which an atom of hydrogen is replaced by the group (NO 2 )'. CH 4 CH 3 (N0 2 ) Methane. Nitromcthane. It is obtained by the action of potassium nitrite upon potas- sium monochloracetate (Kolbe). CII 2 CI.C0 2 K + KNO 2 -I- IPO = KCl + CH 3 (NO' 2 ) + KHCO 3 Potassium mono- Potassium Nitromethane. chloracetate. nitrite. It is also produced by the action of silver nitrite on methyl iodide (V. Meyer). Nitromethane is a liquid boiling between 101 and 102. It has an acid character, and one of its hydrogen atoms may be replaced by sodium. Nitromethane is clearly distinguished from methyl nitrite by the following property : nascent hydrogen transforms nitrome- thane into methylamine, a reaction which does not take place with its isomeride. CH 3 (N0 2 ) + 3H 2 = CH 3 .NH 2 + 2EPO Nitromethane. Methylamine. METHYLNITROLIC ACID. This remarkable combination has been obtained by V. Meyer by the action of nitrous acid upon nitromethane. CH 3 (N0 2 ) + NO.OH = CH ^N-OH + HZ It is seen that in this compound two atoms of hydrogen of the methyl group CH 3 , are removed by an atom of oxygen of the nitrous acid, and replaced by the residue (N.OH). Methylnitrolic acid is prepared by dissolving 5 grammes of nitromethane in water, and adding first a dilute solution of potassium nitrite cooled to 0, then dilute sulphuric acid also cooled to 0, and finally dilute solution of potassium hydrate as long as the red color persists. At this moment, sulphuric acid is again added until the liquid is decolorized ; the solution is then saturated with calcium carbonate, and agitated with ether, which dissolves the methylnitrolic acid. 452 ELEMENTS OF MODERN CHEMISTRY. After the evaporation of the ether, the acid remains as large, transparent, colorless prisms, fusible at 54, but decomposing at the same time into formic acid and nitrogen. Dilute sul- phuric acid decomposes rnethylnitrolic acid into formic acid and nitrogen monoxide. CH 2 N 2 3 = CH 2 2 H- N 2 Formic acid. Nitrogen monoxide. The crystals decompose spontaneously in a few days. FULMINATES OF MERCURY AND SILVER. Among the important compounds related to the more simple organic combinations are those explosive salts known ^fulmi- nates of mercury and silver. They are obtained by dissolving mercury or silver in nitric acid and adding alcohol to the still hot solution. In a few minutes a brisk effervescence takes place, and fulminate of mercury or of silver is deposited as a white, crystalline precip- itate. When dry, these bodies explode violently by either heat or percussion. Fulminate of mercury is the basis of percus- sion-caps. The composition of these salts is interesting; fulminate of mercury contains a monatomic group, (NO 2 ), a cyanogen group, (CN), and an atom of mercury, all three being united to an atom of carbon, of which the four atomicities are thus perfectly satisfied. Fulminate of silver has an analogous composition, but con- tains two atoms of silver. The fulminates may thus be grouped with organic compounds containing one atom of carbon, especially with the cyanide of methyl (Kekule). The following are some of these com- pounds : C H H H H methane. C H H H Gy methyl cyanide. C(N0 2 ) H H H nitromethane. C(N0 2 ) H H Na sodium-nitromethane. C(N0 2 ) H H Cl chloro-nitromethane. C(N0 2 ) Cl Cl Cl trichloro-nitromethane (chloropicrin). C(N0 2 )(N0 2 )(N0 2 )H nitroform. C(N0 2 )* tetranitromethane. C(N0 2 ) Ag Ag Cy fulminate of silver. C(N0 2 ) Hg" Cy fulminate of mercury. CACODYL. 453 CACODYL, OR DIMETHYLARSINE. This interesting compound has long been known in an im- pure state. In 1760, Cadet, demonstrator of chemistry at the Jardin-du-Roi, distilled a mixture of potassium acetate and white arsenic (arsenious oxide). He collected in the receiver an oily liquid, having an extremely offensive odor, and pro- ducing dense white fumes in the air. Hence the name fuming liquor of Cadet. Bunsen's investigation into the chemistry of this body and its combinations has become classic. According to his re- searches, the fuming liquor of Cadet is a mixture of two bodies, one of which, containing only carbon, hydrogen, and arsenic, plays the part of a radical : it is cacodyl ; the other body is the oxide of this radical. To obtain cacodyl in the pure state, the crude product is treated with hydrochloric acid, which converts the oxide of cacodyl into chloride. As 2 (CH 3 ) 4 -f 2HC1 = 2As(CH 3 ) 2 Cl + H 2 Dimethylarsine oxide. Dimethylarsine chloride. This chloride, separated by distillation, and treated with zinc at 100 in sealed tubes, furnishes free cacodyl. The latter is a dense liquid boiling at 170, and having a penetrating arsenical odor. It is very poisonous. It produces dense white fumes in the air, even taking fire spontaneously. Its vapor density is 7.101. According to this vapor density, free cacodyl should be rep- resented by the formula As 2 (CH 3 / = (CH 3 /As-As(CH 3 ) 2 . Arsenic being either triatomic or pentatomic it is seen that cacodyl is not saturated ; hence it can directly fix chlorine, oxygen, etc., yielding two series of compounds. Thus, one molecule of cacodyl, As 2 Me*, can fix 1 or 3 molecules of chlo- rine, forming the two chlorides : As 2 Me* + Cl 3 == 2AsMe 2 Cl As 2 Me* + 3C1 2 = 2AsMe 2 Cl 3 To the two chlorides correspond the bromides, iodides, oxides, sulphates, etc. The oxides are Cacodyl oxide [As(CH3) 2 ] 2 Cacodylic acid As(Cli 3 ) 2 O.OH 454 ELEMENTS OP MODERN CHEMISTRY. Independently of the cacodyl compounds, other combinations of arsenic and methyl are known, the methylarsines and the compounds of methylarsonium. These bodies form two series, which were discovered and studied by Baeyer, and which belong to the type AsX 3 and AsX 5 . The compounds of the first kind are not saturated, and can combine with Cl 2 , or the equivalent of Cl 2 , passing into the state of the saturated compounds of the series AsX 5 . Series AsX 3 Series AsX& As(CH 3 )3 As(CH8)*Cl Triracthylarsinei Tetramethylarsouium chloride. As(CH 3 ) 2 Cl As(CH3)3C12 Dimethylarsine monochloride. Trimetliylarsine dichloride. As(CH 3 )Cl 2 As(CH 3 ) 2 Cl 3 Monomethylarsine dichloride. Dimethylarsine trichloride. AsCl 3 As(CH 3 )Cl* Arsenic trichloride. Monomethylarsine tetrachloride. It is worthy of remark that the trichloride of arsenic is incapable of fixing Cl 2 , and passing into the state of penta- chloride. These compounds need not be described. It may only be mentioned that triinethylarsine, As(CH 3 ) 3 , is formed, together with cacodyl, by the action of methyl iodide on sodium arsenide. It is a liquid boiling below 100. ETHYL COMBINATIONS. The monatomic residue (C 2 H 5 )' = C 2 H 6 H, which is the radical of ordinary alcohol, is called ethyl. Numerous com- pounds are known into which the radical enters. When combined with hydrogen, it forms a gas, C 2 H 6 , which is ethyl hydride or ethane. The chloride, bromide, iodide, and cyanide of ethyl were formerly designated as simple ethers. C 2 H 5 C1 ethyl chloride. C 2 H5Br ethyl bromide. CWl ethyl iodide. C 3 H.CN ethyl cyanide. Ordinary alcohol is the hydrate, ether is the oxide of ethyl. C 2 HM)H ethyl hydrate (alcohol). C 2 H 5 -0-C 2 H5 = (C 2 H 5 ) 2 ethyl oxide (ether). ETHYL HYDRATE. 455 The neutral compound ethers are derived from the corre- sponding acids by the substitution of the radical C 2 H 5 for their basic hydrogen. C 2 H 3 0-OH C 2 H 3 0-OC 2 H* Acetic acid. Ethyl acetate. P202 I OH P202 I ' C2H5 3 1 OH 3 1 O.C2R5 Oxalic acid. Ethyl oxalate. fOH (O.C'H* PO^OH PO^O.C 2 H5 (OH (o.c 2 H5 Phosphoric acid. Phosphoric ether (triothyl phosphate). Ethyl exists in the most diverse combinations. It can re- place the hydrogen of ammonia, forming ethylated bases. It can unite with the metalloids and metals. Free Ethyl, or Butane, C 4 H 10 . When it is sought to obtain free, ethyl by heating ethyl iodide to 150 with zinc in sealed tubes, the radical combines with itself, its molecule being doubled (Frankland). 2C 2 H 5 I + Zn = Znl 2 + (C 2 H 5 / A gas is thus formed which liquefies at -f-l. It was formerly named free ethyl, but is the hydride of butyl, or butane. Indeed, it is incapable of regenerating ethyl compounds containing the simple radical (C 2 H 9 ). When treated with bro- mine, it yields hydrobromic acid and a bromide C 4 H 8 Br 2 , which, according to Carius, is identical with butylene bromide. Ethyl Hydride, or Ethane, C 2 H 6 = CH 3 -CH 3 . Frank- land obtained this gas by treating zinc-ethyl with water. Zn(C 2 H 5 ) 2 + 2H 2 === 2C 2 H 6 + Zn(OH) 2 Zinc ethyl. Ethane. Zinc hydrate. It is a colorless gas, burning with a slightly blue, luminous flame. When treated with chlorine, it yields ethyl chloride and hydrochloric acid. ETHYL HYDRATE, OR ALCOHOL. C 2 HO == CH 3 -CH 2 .OII Alcohol is the product of the fermentation of solutions which contain glucose, or a substance capable of transformation into glucose. It may be formed synthetically in various manners: 1. By passing ethylene gas into sulphuric acid (Hennel and 456 ELEMENTS OP MODERN CHEMISTRY. Faraday) and boiling the ethylsulphuric acid so formed (Ber- thelot). PITTS 1 C 2 H 4 + H 2 g Q4 = !g 4 Ethylene. Ethylsulphuric acid. SO 4 + H 2 = C 2 H 5 .OH + H 2 SO* Ethylsulphuric acid. Alcohol. 2. By heating ethylene gas with hydriodic acid and decom- posing the ethyl iodide so formed with potassium hydrate (Ber- thelot). C 2 H 4 -f HI == C 2 H 8 I C 2 H 5 I + KOH == C 2 H 5 .OH + KI 3. By bringing aldehyde in contact with sodium amalgam in presence of water. The nascent hydrogen formed in this case fixes upon the aldehyde, converting it into alcohol (A. Wurtz). C 2 H<0 -f H 2 = C 2 H 6 Aldehyde. Alcohol. Preparation and Purification of Alcohol Alcohol is manufactured by distilling fermented liquors, such as wine, fermented juice of beet>roots, and the product obtained from the fermentation of malt, which is saccharified barley, corn, or other grain. The apparatus now used for this operation has reached such a degree of perfection that alcohol of 95 per cent. may be obtained immediately by one distillation. Absolutely pure alcohol is obtained by rectifying the alcohol of commerce over substances avid of water, such as anhydrous potassium carbonate, quick-lime, or caustic baryta. The last portions of water are removed, and absolute alcohol obtained by redistilling the rectified alcohol with caustic baryta. Or some sodium may be dissolved in the alcohol, which may then be rectified on a water-bath. Properties. Alcohol is a colorless, mobile liquid, having an agreeable, spirituous odor. Density at 0, 0.8095. Boiling- point, 78.4 at the normal pressure. Alcohol mixes with water and ether in all proportions. Its mixture with water takes place with elevation of temperature and contraction of volume. The maximum contraction takes place when the two bodies are mixed in the proportion of one molecule of alcohol (53.94 parts) to three molecules of water (49.84 parts). ETHYL HYDRATE. 457 Alcohol absorbs moisture when exposed to the air. It dis- solves many gases, liquids, and solids. Tinctures are solutions of various medicinal substances in alcohol. Among the simple bodies which are soluble in alcohol may be mentioned iodine. Potassium and sodium hydrates dissolve in it readily, and it is the same with most of the mineral acids. Many of the chlorides are soluble in alcohol ; such are those of calcium, strontium, zinc, and cadmium, ferric, cupric, mercuric, and auric chlorides. Alcohol dissolves the natural alkaloids, the essential oils, resins, and fatty bodies, the latter, however, less readily than ether. Decompositions. When vapor of alcohol is passed through a red-hot porcelain tube, it is decomposed into water, carbon monoxide, hydrogen, methane, and ethylene. Besides this, carbon is deposited in the porcelain tube, and a small quantity of naphthaline is produced (Th. de Saussure), as well as benzol and phenol (Berthelot). The principal products of the decomposition of alcohol at a dull-red heat are methane, hydrogen, and carbon monoxide. C 2 H 6 = CO + CH 4 -f H 2 On the application of a burning body, alcohol takes fire and burns with a slightly luminous, bluish flame. On contact with platinum black, alcohol vapor mixed with air undergoes a slow combustion, which produces successively aldehyde and acetic acid. C 2 H 6 + O = C 2 H*O + H 2 Alcohol. Aldehyde. C 2 H 4 + = C 2 H 4 2 Aldehyde. Acetic Acid. Acetic ether and a small quantity of a volatile, neutral body, called acetal, are at the same time formed as accessory products (Stas). The lamp without flame of Dobereiner depends upon the slow combustion of alcohol. The wick of an ordinary spirit- lamp is surmounted by a spiral of platinum wire, so that when the lamp is lighted the spiral is heated to incandescence. If then the flame be extinguished, by covering it for an instant with a test-tube, the alcohol vapor continues to rise with the air around the still hot spiral, and undergoes a slow combustion. But the latter develops heat, and the spiral rapidly becomes u 39 458 ELEMENTS OF MODERN CHEMISTRY. heated to incandescence, and if the current of air be regulated by a small glass chimney, the experiment may continue as long as the wick emits vapor of alcohol in sufficient quantity. Bodies rich in oxygen oxidize alcohol at ordinary tempera- tures ; such are chloric and chromic acids. If a little alcohol be poured upon some chromic acid placed upon a brick, the liquid is immediately inflamed and the chromic acid reduced to chromium oxide. Chlorine attacks alcohol with great energy, the final product of the reaction being a body which has received the name chloral (Liebig, Dumas). If a small piece of potassium or sodium be thrown into pure alcohol, the metal soon melts, and then dissolves with disen- gagement of hydrogen. The product of the reaction is a crys- talline, solid matter which is ethylate of potassium or sodium, that is, a body derived from alcohol by the substitution of an atom of an alkaline metal for an atom of hydrogen. K Na Alcohol. Potassium ethylate. Sodium ethylate. Uses of Alcohol, Alcohol is used as a combustible in spirit- lamps. In the arts, it is employed in the manufacture of ether, chloroform, eau de cologne, and many other products. It is largely used in the laboratory, and in pharmacy, as a solvent ; it serves for the preservation of anatomical specimens. In France and England, alcohol employed for certain industrial uses is exempted from part of the tax, when it has previously been mixed with about one-tenth of wood-spirit and a few per cent, of mineral oils and resin. Such a mixture is unfit for the manufacture of brandy and liquors, but its usefulness as a solvent is in many cases unimpaired. Alcohol exists in fermented liquors, such as wine, cider, and beer. It is contained in much larger quantities in brandies, whiskeys, and spirits. These are products of the distillation of various alcoholic liquids. They are more or less rich in alco- hol. Brandy is prepared by the distillation of wine, cider, or the products of fermentation of cherry-juice (cherry-brandy), sugar-cane (rum), beet-root molasses (beet-brandy). Whiskey is distilled from fermented starchy materials, such as corn, rye, potatoes, etc., the starch being first saccharified. The richness of these materials in alcohol is indicated by the degrees of an ETHYL OXIDE. 459 alcoholometer. The following table gives the strength of some of these liquors. PERCENTAGE OF CAR-TIER'S AREOMETER. ALCOHOL. BY VOLUME. Weak brandy ......... 16 37.9 Proof spirits ......... 19 50.1 Strong brandy . . . . ..... 22 59.2 Ordinary alcohol ........ 33 85.1 Rectified alcohol (strongest commercial) 40 95. Absolute alcohol ........ 41.2 100. ETHYL OXIDE, OR ETHER. If ethyl iodide be added to an alcoholic solution of ethylate of sodium and a gentle heat be applied, a deposit of sodium iodide is formed and vapors are disengaged which may be con- densed in a cooled receiver into an ethereal liquid. It is oxide of ethyl. C'H'I + Etliyl iodide. Sodium ethylate. Ethyl oxide. If, in the preceding experiment, the ethyl iodide be replaced by methyl iodide, an extremely volatile liquid will be formed, which is the double oxide of methyl and ethyl. CH3I + _ Nal + Methyl iodide. Oxide of methyl and ethyl. These classic experiments, due to Williamson, show that the oxide of ethyl contains two ethyl groups. It may be regarded as alcohol in which the hydrogen atom of the group hydroxyl is replaced by ethyl. H-O-H C 2 H 5 -0-H C 2 H 5 -0-C 2 H 5 Water. Alcohol. Ethyl oxide. Preparation. Ether is prepared in the arts by the action of sulphuric acid on alcohol. A mixture of 9 parts of con- centrated sulphuric acid and 5 parts of alcohol of 90 per cent. is heated in a flask, A (Fig. 122), and a small, continuous stream of alcohol is allowed to flow into this mixture through the funnel-tube a. The temperature of the liquid, indicated by the thermometer , should not exceed 140 or 145. The vapOr disengaged is condensed in a Liebig's condenser, B, through which a stream of cold water flows continually. Under these 460 ELEMENTS OF MODERN CHEMISTRY. conditions, a mixture of ether and water collects in the re- ceiver D, together with a little alcohol, and towards the close of the operation, a small quantity of sulphurous acid gas is disengaged. The product is purified by washing with milk of lime, and then with pure water, after which it is rectified over calcium chloride on a water-bath. Fig. 122 represents the apparatus used for public demonstration ; in the arts, the opera- tion is conducted on a large scale in apparatus of an analogous construction. FIG. 122. Theory of Etherification. The transformation of alcohol into ether is a true dehydration, brought about by the sul- phuric acid. 2(C 2 H 5 .OH) = (C 2 H 5 ) 2 + H 2 Williamson clearly proved that it is effected in two distinct phases ; in the first, ethylsulphuric acid and water are formed. C!H H> Alcohol. H 2 Sulphuric acid. Ethylsulphuric acid. ETHYL OXIDE. 461 In the second, another molecule of alcohol reacts with the ethylsulphuric acid; ether is formed and sulphuric acid is regenerated. Ethylsulphuric acid. Alcohol. Ether. Sulphuric acid. Hence the ether and water collected in the receiver are pro- ducts of two distinct phases of the reaction. Ethylsulphuric acid is continually formed and as continually decomposed, regenerating sulphuric acid ready to act upon new por- tions of alcohol. However, although the operation is con- tinuous, it cannot go on indefinitely, for the mixture blackens after a time and becomes unfit to etherify new quantities of alcohol. Properties of Ether. Ether is a colorless, very mobile liquid ; its taste is at first burning, then cooling ; its odor is suave and agreeable, and is called ethereal. Density at 0, 0.7366. Boiling-point under the normal pressure, 34.5. It is but slightly miscible with water, on the surface of which it forms a separate layer. 9 parts of water dissolve 1 part of ether ; 36 parts of ether dissolve 1 part of water. Ether dis- solves in all proportions in alcohol and in methyl alcohol. It slightly dissolves sulphur and phosphorus, and notable quantities of bromine, iodine, ferric, mercuric, and auric chlo- rides, and many organic bodies, such as the oils, fats, resins, alkaloids, etc. It is very inflammable and burns with a quite luminous flame. Its vapor explodes violently when mixed with air or oxygen and ignited. If a heated spiral of platinum wire be suspended in a glass jar containing a little ether, in such a manner that the lower extremity of the wire is but a little distance from the surface of the liquid, the wire will soon become brightly incandescent and will ignite the ether. This effect is due to the ether vapor, which, coming in con- tact with the platinum, and being mixed with air, undergoes a slow combustion. Heat is thus developed, and the wire be- comes incandescent. Chlorine acts on ether with extreme energy. If the action be moderated, various products of substitution are obtained, among which the following have been well studied : 39* 462 ELEMENTS OF MODERN CHEMISTRY. Monochlorether (2H5>0 liquid boilin S at 98-99. Dichlorether C2 ^ 3 2H5> li( l uid boiling at 140-147. r^2H3p]2 Tetrachlorether l^ li( l uid density 1.5. Perchlorether 25 ^ > ^ colorless crystals, fusible at 69. The last is a solid body, crystallizing in octahedra. By the action of heat it is decomposed into carbon sesquichloride and perchloraldehyde (Malaguti). + C*C1*0 Perchlorether. Carbou sesquichloride. Perchloraldehyde. When two parts of bromine are added to one part of ether, and the mixture is cooled, a garnet-colored liquid separates and soon crystallizes. It is a compound of bromine and ether, (C 2 H 5 ) 2 O.Br 2 , which crystallizes in thin, red plates, fusible at 22 ; it is easily decomposed (Schiitzenberger). SULPHYDRATE AND SULPHIDE OF ETHYL. Two bodies are known which are intimately related, as re- gards their constitutions, with alcohol and ether. They are the sulphydrate and the sulphide of ethyl. The first, formerly known as mercaptan, represents alcohol containing an atom of sulphur instead of an atom of oxygen ; the second represents ether in which the oxygen atom is replaced by sulphur. C 2 H 5 .OH (C 2 H 5 ) 2 O Ethyl hydrate. Ethyl oxide. C 2 H 5 .SH (C 2 H 5 ) 2 S Ethyl sulphydrate. Ethyl sulphide. Ethyl sulphydrate is obtained by distilling a concentrated aqueous solution of potassium sulphydrate with a solution of potassium ethylsulphate. It may also be prepared by passing vapor of ethyl chloride into an alcoholic solution of potassium sulphydrate. The liquid is distilled as soon as it is saturated with ethyl chloride, and water is added to the distillate. Ethyl sulphydrate separates. KSH + C 2 H 5 C1 = KC1 + CTP.SH Potassium sulphydrate. Ethyl chloride. Ethyl sulphydrate. ETHYL CHLORIDE. 463 Ethyl sulphydrate is a transparent, colorless liquid, very mo- bile, and having a fetid odor. Density at 21, 0.835. Boil- ing-point, 36.2 (Liebig). It reacts energetically with mercuric oxide, forming water and a white, crystalline body which represents ethyl sulphy- drate in which the hydrogen is replaced by mercury. Hence the name mercaptan (mercurium captans), given to the sulphy- drate of ethyl by Zeise. This mercuric compound is insoluble in water; it contains (C 2 IPS) 2 Hg". Ethyl sulphide is obtained, like the sulphydrate, by double decomposition. Vapor of ethyl chloride is passed into an alco- holic solution of potassium monosulphide. K 2 S + 2C 2 H 5 C1 = 2KC1 + (C 2 H 5 ) 2 S Potassium sulphide. Ethyl chloride. Ethyl sulphide. Ethyl sulphide is a colorless liquid, having a garlicky odor. It boils at 75. It is insoluble in water. ETHYL CHLORIDE. C 2 H 5 C1 This body is prepared by saturating alcohol with hydrochloric acid gas and distilling on a water-bath. Ethyl chloride is dis- engaged, and should be passed first through a wash-bottle and then through a tube containing calcium chloride, after which it may be condensed in a receiver placed in a freezing mixture. Below 11 ethyl chloride is a mobile, colorless liquid, having a penetrating and agreeable odor. It boils at 11 ; it is inflam- mable, and burns with a flame tinged with green. If some solution of silver nitrate be agitated in a jar con- taining vapor of ethyl chloride, no precipitate will be formed ; but if the agitation be continued after the vapor has been ignited, an abundant precipitate of silver chloride will be formed, owing to decomposition of the silver nitrate by the hy- drochloric acid produced by combustion of the ethyl chloride. Ethyl chloride produces a precipitate of silver chloride when passed into an alcoholic solution of silver nitrate. Chlorinated Derivatives of Ethyl Chloride. When ethyl chloride is submitted to the action of chlorine, various com- pounds are successively formed by the substitution of chlorine for hydrogen, atom for atom. The following is the nomencla- 464 ELEMENTS OF MODERN CHEMIETRY. ture and composition of these chlorinated compounds, which were discovered by V. Regnault. C 2 H5CI ethyl chloride. C 2 H*C1 2 dichlorethane (ethylidine chloride) boils at 57.5. C 2 H 3 CI 3 trichlorethane boils at 75. C 2 H2C1* tetrachlorethane boils at 127.5. C 2 HC1 5 pentachlorethane boils at 158. C 2 C1 6 hexachlorethane (sesquichloride of carbon). It will be noticed that the second of these compounds is isomeric with ethylene chloride, or Dutch liquid, of which the description will be found farther on. It may be obtained by treating aldehyde with phosphorus pentachloride. CH 3 -CHO + PCI 5 = CH 3 -CHC1 2 -f POOP Aldehyde. Dichlorethane. Phosphorus oxychloride. This mode of formation indicates its constitution, which is expressed by the formula CH 3 CHOP To distinguish it from its isomeride ethylene chloride, CH 2 C1 CH 2 C1 it is named dichlorethane or ethylidene chloride. In the sesquichloride of carbon, C 2 C1 6 , the hydrogen atoms are all replaced by chlorine. Carbon sesquichloride is a crys- stalline solid, melting at 162, and boiling at 182 (Faraday). ETHYL IODIDE. This important compound is prepared by the action of alco- hol on iodine in presence of amorphous phosphorus. Phos- phorus iodide is formed, and reacts upon the alcohol, yielding ethyl iodide and an acid of phosphorus. The former distils into the receiver, together with the alcohol which escapes the reaction. Water is added, and the lower layer of liquid is separated, dried with calcium chloride, and rectified on a water- bath. Ethyl iodide is a colorless liquid, but becomes brown when long kept, especially when exposed to light. Density at 0, 1.9753. Boiling-point, 72.2. ETHYL CYANIDE. 465 It can exchange its iodine by double decomposition, as can potassium iodide. If ethyl iodide be added to an alcoholic solution of silver nitrate, a yellow precipitate of silver iodide is at once formed, while ethyl nitrate remains in solution. C 2 H 5 I -|- AgNO 3 = Agl + (C 2 H 5 )NO 3 Ethyl iodide. Silver nitrate. Ethyl nitrate. ETHYL CYANIDE. This compound is formed when ammonium propionate is distilled with phosphoric anhydride. (NH 4 )C*H 8 O 1 = OTPN + 2H 2 Ammonium propionate. Ethyl cyanide. From this mode of formation, ethyl cyanide is sometimes called propionitrile. The same body exists in the product of the distillation of a mixture of potassium cyanide and potassium ethylsulphate. KCN + C2I ^>SO* = >SO* + C2H5 - CN Potassium Potassium Potassium Ethyl cyanide. cyanide. ethylsulphate. sulphate. But this product, which is liquid and has a variable boiling- point, contains, independently of the true cyanide of ethyl, an isomeride of that body, whose existence was foreseen by Meyer and discovered by Gautier in the product of the action of ethyl iodide on silver cyanide. Ethyl cyanide is a colorless liquid having a penetrating and pleasant odor. It boils at 96.*7 When it is boiled with potassium hydrate, potassium propio- nate is formed and ammonia is disengaged (Dumas, Malaguti, and Le Blanc). C 3 H 5 N -|- KOH + H 2 = KC 3 H 5 O 2 + NH S Ethyl cyanide. Potassium propionate. When ethyl cyanide is brought into contact with dilute sul- phuric acid and zinc, it fixes 4 atoms of hydrogen and is converted into propylamine (Mendius). C4PN + H* = C 3 H 9 N Ethyl cyanide. Propylamine. Ethylcarbylamine. This name was given by Gautier to the isomeride of ethyl cyanide already mentioned. It is a color- less liquid, having a very penetrating and intensely offensive u* 466 ELEMENTS OF MODERN CHEMISTRY. odor. It boils at 79. With potassium hydrate it yields po- tassium formate and ethylamine. * + KOH + H 2 = H N -I- ECHO 2 H/ Ethylcarbylamiae. Ethylamine. Potassium formate. ETHYL NITRITE, OR NITROUS ETHER. C 2 H 5 .O-NO This compound is obtained by the action of nitric acid on alcohol. The reaction is very violent, and abundant red vapors are evolved. After passing through a wash-bottle, they are conducted into a well- cooled receiver, where the ethyl nitrite condenses. It is a yellowish, very volatile liquid, whose odor recalls that of apples. It boils at 18. It is but slightly soluble in water. Hot water immediately decomposes it into alcohol and nitrous acid, the latter being itself decomposed into nitric acid and nitrogen dioxide. NITRETHANE AND ITS DERIVATIVES. C 2 H*-NO 2 This isomeride of ethyl nitrite represents ethane, C 2 H 6 , in which one atom of hydrogen is replaced by the group (NO 2 )'. It is the superior homologue of nitromethane. It is obtained, together with a certain quantity of ethyl nitrite, when ethyl iodide is treated with silver nitrite. C 2 H 5 I -f AgNO 2 = C 2 H 5 (N0 2 ) + Agl Ethyl iodide. Silver nitrite. Nitrethane. It is a liquid having a peculiar, ethereal odor and boiling at 113-114. Density at 13, 1.0582 (V. Meyer). With nascent hydrogen, it furnishes pure ethylamine. C 2 H 3 (N0 2 ) + 3H 2 =; C 2 H 5 (NH 2 ) + 2H 2 All of the homologues of nitrethane thus yield the corre- sponding amines. It is a general character of the nitro com- pounds, and one which is not possessed by their isomerides, the nitrous ethers. In constitution and properties, nitrethane ETHYL NITRATE. 46*7 approaches nitrobenzol, as will be seen by the following com- parison of their formulae: C 2 H 5 .H C 6 H 5 .H Ethane. Benzol. C 2 H 5 (N0 2 ) C 6 H 5 (N0 2 ) Nitrethane. Nitrobenzol. C 2 H 5 (NH 2 ) C 6 H 5 (NH 2 ) Ethylamine. Phenylamine (aniline). The presence of the group (NO 2 ) confers acid properties NO 2 upon nitrethane. Its sodium compound, C 2 !! 4 ^^ , is formed either by the action of an alcoholic solution of sodium hydrate on nitrethane, or by the direct action of sodium on the same body; in the latter case hydrogen is disengaged. Sodium- nitrethane is very explosive (V. Meyer and Stuber). When it is sought to prepare potassium-nitrethane by the action of alcoholic potassium hydrate on nitrethane, the latter body is decomposed, yielding, among other products, potassium nitrite. Now, the latter salt exerts a remarkable action on ni- trethane, giving rise to a new body of complex composition, potassium ethylnitrolate. Ethylnitrolic acid may be obtained by a process analogous to that which has been described for the preparation of methyl- nitrolic acid. Ethylnitrolic acid contains CH 3 C-N.OH NO 2 It crystallizes in light-yellow, transparent prisms, possessing a feeble bluish fluorescence and a very sweet taste. It decom- poses without violence at 81-82 into nitrogen, nitrous vapors, and acetic acid. When boiled with dilute sulphuric acid, it decomposes into acetic acid and nitrogen monoxide. C 2 H 4 N 2 3 = C 2 H 4 2 + N 2 Ethylnitrolic acid. Acetic acid. ETHYL NITRATE, OR NITRIC ETHER. (C 2 H5)NO 3 This is obtained by the action of nitric acid upon alcohol in presence of a small quantity of urea. The latter body prevents the reduction of the nitric acid to nitrous acid. Nitric ether 468 ELEMENTS OF MODERN CHEMISTRY. condenses in the receiver. It is washed with water, dehydrated with calcium chloride, and rectified. It is a liquid, having an agreeable, ethereal odor. It boils at 86. Density at 0, 1.1322. Potassium hydrate decomposes it, like all compound ethers, forming potassium nitrate and alcohol. (C 2 H 5 )N0 3 + KOH C 2 H 5 .OH + KNO 3 It dissolves in ammonia, especially if the latter be warm, yielding ammonium nitrate and ethylamine. The reaction is analogous to that of ammonia upon methyl nitrate. ETHYL CYANATE. C 2 H 5 -N=CO This compound is prepared by distilling on an oil-bath a mixture of 2 parts of potassium ethylsulphate and 1 part of recently-prepared and well-dried potassium cyanate. The pro- duct which condenses in the receiver is rectified on a water- bath (Wurtz). Ethyl cyanate is a colorless liquid, having a very irritating odor. It boils at 60. Potassium hydrate de- composes it into carbonic acid gas and ethylamine. It com- bines with ammonia, developing heat and producing ethylurea (page 443). The bodies which have until now been known as cyanic acid and ethyl cyanate, are only isomerides of the oxygen com- pounds of cyanogen. They should be named isocyanic acid and isocyanate of ethyl. The true cyanic ether, (C 2 H 5 .O)CN, or rather a polymeride of that body, has been obtained by Cloe'z. It is formed by the action of cyanogen chloride on ethylate of sodium. CNC1 + Na.OC 2 H 5 = CN.OC 2 H 5 + NaCl Cyanogen chloride. Sodium ethylate. Ethyl cyanate. Potassium hydrate decomposes the true ethyl cyanate, like all other compound ethers, into alcohol and the corresponding potassium salt (cyanate). ETHYLSULPHURIC, OR SULPHOVINIC ACID. H HO This body is an example of an acid ether. It results from the substitution of a single ethyl group for one atom of hydro- gen in sulphuric acid, which is dibasic. ETHYL CARBONATE. 469 H) P) so* It is formed by the action of sulphuric acid upon alcohol. The mixture of the two bodies becomes hot, and if after cool- ing the liquid be diluted and saturated with barium carbonate, an abundant precipitate of barium sulphate will be formed, and a soluble salt of barium, the ethylsulphate, will remain in solu- tion. A solution of ethylsulphuric acid may be obtained by exactly decomposing this salt with dilute sulphuric acid. By boiling, ethylsulphuric acid is decomposed into sulphuric acid and alcohol. The ethylsulphates are beautiful salts ; they are crystalliz- able and soluble in water. Ethyl Sulphate. ^5 } SO* = ^5 '^>S0 2 . This body, which represents sulphuric acid in which the two atoms of hydrogen are replaced by two ethyl groups, is formed when vapor of sulphuric anhydride is passed into ether cooled in a freezing mixture (Wetherill). (C 2 H 5 ) 2 + SO 3 = (C 2 H 5 ) W It is an oily liquid having an acrid taste. Its density is 1.120. It cannot be distilled. ETHYL CARBONATE. C 2 H5 ) . Ettling obtained this compound by introducing potassium or sodium little by little into ethyl oxalate heated to 130. The metal dissolves, disengaging carbon monoxide. A brown mass is obtained, which must be distilled with water. The ethyl car- bonate which passes over is dehydrated with calcium chloride and distilled. It may also be obtained by double decomposition by heating ethyl iodide with silver carbonate. Ethyl carbonate is a colorless liquid, having a pleasant, ethe- real odor ; its density at is 0.9998, and it boils at '125. 40 470 ELEMENTS OP MODERN CHEMISTRY. In the cold, ammonia converts it into ethyl carbamate, or methane. C*H:0> 00 * NH3 = C*H5 H 2 > CO + C2H5 ' OH Ethyl carbonate. Ethyl carbamate. It yields urea and alcohol when heated to 100 with am- monia. ' Ethyl carbonate. Urea. ETHYL CHLOROCARBONATE. OTlSx* Dumas obtained this ether by passing chlorocarbonic gas into alcohol. Water is added to the product of the reaction, and the insoluble liquid is separated, dried, and distilled. PI PI cJ>CO + C2R5.0H = HC1 + C2H 5o>CO Chlorocarbonic gas. Ethyl chlorocarbonate. It is a liquid having a pungent, ethereal odor. It boils at 94. Hot water decomposes it. Ammonia converts it into ethyl carbamate, or urethane. SERIES OF SATURATED HYDROCARBONS. C 2 H 2n + 2 To methane and ethane, which have already been described, are related numerous hydrocarbons belonging to the same series, C n H 2n+2 . They are called saturated because no hydro- carbons are known in which the number of hydrogen atoms exceeds that indicated by the preceding formula. Again, the hydrocarbons in question can fix directly no other atoms. For example, in order that chlorine can enter into one of their molecules, hydrogen must first be removed, and this displace- ment is known to take place, atom for atom, according to the law of substitution. Thus, if chlorine be made to act upon the hydrocarbon C 6 H U (hexane), the compounds C*H 13 C1, C G H 12 C1 2 , C 6 H"C1 8 , maybe obtained successively. Let us con- sider the first of these compounds, C 6 H 18 C1. The Cl may be replaced by the group OH, and the chloride is thus converted SATURATED HYDROCARBONS. 4*71 into an alcohol. For this purpose the chloride is caused to react with a silver salt, the acetate, for example, and hexyl acetate is formed by double decomposition. C 6 H 13 C1 -f AgC 2 H 3 2 = C 6 H 13 .C 2 H 3 2 + AgCl Hexlyl chloride. Silver acetate. Hexyl acetate. Boiling potassium hydrate will transform this ether into hexyl hydrate. C 6 H 13 .C 2 H 3 2 + KOH = KC 2 H 3 2 + C 6 H 13 .OH Hexyl acetate. Potassium acetate. Hexyl hydrate. This series of reactions permits of the successive transforma- tion of any hydrocarbon of the saturated series into a chloride, an acetate, and a hydrate, and the latter is the alcohol corre- sponding to the hydrocarbon. The following is the series of saturated hydrocarbons : CH* methane. C 2 H<5 ethane. C 3 H 8 propane. butanes. pentanes, hexanes, C 7 I1 16 heptanes, C 8 H!8 octanes. C 9 !! 20 nonanes. C10H23 deoanes, etc. All of these hydrocarbons, after the fourth of the series, up to the term C 16 H 3 *, have been obtained from petroleum and the products of distillation of bitumen and peat. Towards the close of the distillation, when the temperature passes above 300, the products which distil condense to a solid mass on cooling. When properly purified, this solid forms a colorless, translucent mass, which has received the name paraffin. It is probably a mixture of several hydrocarbons of the series C n H 2ll+2 . Its point of fusion varies between 45 and 65. All of the compounds belonging to this series cannot be described here, but we may briefly consider their constitution. The third member of the series, propane, C 3 H 8 , has the con- stitution indicated by the formula CH 3 -CH 2 -CH 3 . It is a gas which liquefies at 1*7. Its superior homologue, butane, C 4 H 10 , has the constitution CH 3 -CH 2 -CH 2 -CH 3 , and can be obtained by the action of zinc or sodium on ethyl iodide. 2C 2 H 5 I + Na 2 = 2NaI + C*H 10 It is a colorless gas, condensable at -j-l. But we have 472 ELEMENTS OF MODERN CHEMISTRY. here a remarkable instance of isomerism. There is another butane, isomeric with the preceding, and having the consti- CH 3 tution expressed by the formula CH 3 -CH<^ n TT 3 , It is tri- LtL methyl-methane, CH(CH 3 ) 3 , while normal butane is dimethyl- ethane, C 2 H*(CH 3 /, or propyl-methane, CH 3 (C 3 H 7 ). The sig- nification of these words and formulae is evident. Trimethyl- methane is methane, CH 4 , in which three atoms of hydrogen are replaced by three methyl groups. The difference in the atomic grouping is attended by a difference in properties. Trimethyl-niethane is a gas which condenses only at 17. The succeeding terms of the series present isomerisms of the same kind, but much more numerous as their molecular complication is greater. They need not be described here, since the same general principles apply to all. SERIES OF ALCOHOLS. Ethyl alcohol, of which the more important compounds have been briefly described, is not the only product of the fer- mentation of saccharine liquids. Other alcohols are formed in small quantity in this reaction, which is conducted on an exten- sive scale in the arts. Among these alcohols of fermentation are the following : Propyl alcohol, or propyl hydrate, C 8 H 7 .T)H Butyl alcohol, or butyl hydrate, C*H 9 .OH Amyl alcohol, or amyl hydrate, C 5 H n .OH Hexyl alcohol, or hexyl hydrate, C 6 H 13 .OH Heptyl alcohol, or heptyl hydrate, C 7 H l &.OH To each of these alcohols correspond numerous ethereal com- pounds in which the groups propyl, C 3 H 7 , butyl, C 4 H 9 , amyl, C 5 H U , etc., are substituted for the hydrogen of the hydracids and oxacids. To each of those alcohols correspond also an aldehyde and an acid, just as ordinary aldehyde and acetic acid correspond to ordinary alcohol or ethyl hydrate. CH 3 CH 3 CH CH2.0H CHO CO.OH Alcohol. Aldehyde. Acetic acid. CH2-CH 3 CH 2 -CH 8 CH 2 -CH 3 CR2.0H CHO CO.OH Propyl alcohol. Propyl aldehyde. Propionic acid. C 3 H 7 CR20H CHO CO.OH Butyl alcohol. Butyric aldehyde Butyric acid. SERIES OF ALCOHOLS. 473 All of these alcohols contain a group CH 2 .OH united to a group or radical, C n H 2n+1 . When they are converted by oxi- dation into aldehydes and acids, the group CH 2 .OH is trans- formed into a group CHO, characteristic of the aldehydes, or a group CO. OH, characteristic of the acids. These alcohols are said to be primary. Beginning with butyl alcohol, the primary alcohols may have several isomeric modifications, as will be seen shortly. Independently of the primary alcohols, there are others, isomeric with the preceding, but distinguished from them by the fact that they do not yield corresponding aldehydes and acids when oxidized. These iso-alcohols are divided into secondary, which contain the group CH.OH, and tertiary, which contain the group C.OH (Kolbe). Without entering into the details of this subject, we may cite two examples : 1 . By the action of nascent hydrogen upon acetone, Friedel obtained isopropyl alcohol. Gils CH 3 CO + H* = CH.OH CH 3 CH 3 Acetone. Isopropyl alcohol. By oxidation of this iso-alcohol, which is a secondary alcohol (containing the group CH.OH), acetone is again reproduced. CH 3 CH 3 CH.OH + = : H20 + CO CH 3 CH 3 2. Boutlerow discovered an isomeride of butyl alcohol, and named it tertiary butyl alcohol; its constitution is expressed by the formula CH 3 CH3-C.OH CH 3 This alcohol contains, as is seen, the group C.OH. It yields neither aldehyde nor acid by oxidation. In the primary alcohols, the OH is united to a C which is combined with only one other carbon atom ; in the secondary alcohols, to a C united to two other carbon atoms ; while in the tertiary alcohols, the C to which the hydroxyl is attached is joined to three other atoms of carbon. 40* 474 ELEMENTS OF MODERN CHEMISTRY. Propyl Alcohol, C 3 H 8 = CH 3 -CH 2 -CH 2 .OH. This was discovered by Chancel in the oily liquid remaining after the dis- tillation of brandy. It is a spirituous liquid, boiling at 98. Its iodide, C 3 H 7 I, boils at 104.5 (I. Pierre and Puchot). The isopropyl alcohol of Friedel is formed under the circum- stances just indicated. Its constitution is expressed by the formula CH 3 -CH.OH-CH 3 It boils at 86. When propylene gas is heated with hydri- bodic acid, isopropyl iodide, C 3 H 7 I, is obtained, boiling at 92. C 3 H 6 + HI = C 3 H'I Propylene. Isopropyl iodide. Silva has described numerous derivatives of isopropyl alco- hol. Butyl Alcohols, C*H 10 0. The constitution of the butyl alcohol of fermentation, which is a primary alcohol, is expressed riTT3 by the formula pg 3 >CH-CH 2 .OH. It is isobutyl alcohol. In 1852, Wurtz obtained it from the fusel-oil from the rec- tification of beet-root alcohol. It is a colorless liquid, having a penetrating odor analogous to that of amyl alcohol, but more spirituous. It dissolves in 10.5 times its volume of water. It boils at 109, and yields on oxidation an acid isomeric with butyric acid and called isobutyric. It may be regarded as ordinary alcohol in which two atoms of hydrogen are replaced by two methyl groups. CH3 CH(CH3)2 CH 2 .OH CH 2 .OH Alcohol. Isobutyl alcohol. Lieben discovered normal butyl alcohol, isomeric with the alcohol of fermentation, and which yields butyric aldehyde and butyric acid by oxidation. He obtained this alcohol by the action of sodium amalgam in presence of water on butyral (butyric aldehyde). i + H 2 = i CHO CH 2 .OH Butyral. Normal butyl alcohol. De Luynes obtained another isomeride of butyl alcohol by the reduction of erythrite (page 565). This alcohol is second- ary, having the constitution CH 3 -CH 2 -CH(OH)-CH 3 . It SERIES OF ALCOHOLS. 475 boils at 116.9 (Lieben). The corresponding iodide, CH 3 - CH 2 -CHI-CH 3 , boils at 118. It is formed by the following reaction : C*H 10 4 + 7HI == OH 9 I + 4H 2 + 3I 2 Erythrite. Secondary butyl iodide. The tertiary butyl alcohol discovered by Boutlerow has re- ceived the name trimethylcarbinol, on account of its constitu- tion, which has already been indicated. It is a well-crystallized compound, melting between 20 and 25. In conclusion, four alcohols are known having the composi- tion C 4 H 10 0, and presenting a remarkable instance of isomer- ism. Their constitutions are again indicated in the following formulae : CH 3 CH 3 CH 3 CH 3 CH 2 CH 3 -CH CH 2 CH 3 -C.OH CH 2 CH 2 .OH CH.OH CH 3 CH 2 .OH CH 3 Normal primary Primary isobutyl Secondary butyl Tertiary butyl butyl alcohol, alcohol (fermentation). alcoliol. alcohol. (Lieben.) (Wurtz.) (De Luynes.) (Boutlerow.) PTJ3 Amyl Alcohol of Fermentation C 5 H 12 O = CH 3>CH ~ CH 2 -CH 2 .OH. This is the most abundant constituent of fusel-oil from beet-root and potatoes, as well as of that from the marc of grapes, from whiskey, etc. These products are only the residues of the distillation of alcohol from various sources. Amyl alcohol is a colorless liquid, having a rather unpleasant odor. It boils at 132. Its density at 15 is 0.8184. It is nearly insoluble in water. It turns the plane of polarization to the left. There is, nevertheless, an amyl alcohol which has no action upon polarized light, and which Pasteur has named inactive amyl alcohol. The latter boils at 130. It is iso- meric with the amyl alcohol of fermentation, from which it differs in physical properties, but presents the same composi- tion and the same chemical properties. It is a case of physical isomerism. When submitted to the action of zinc chloride, amyl alcohol is converted into amylene and polymerides of that body (di- amylene, C 10 H 20 , triamylene, C 15 H :io ). C 5 H 12 = C 5 H 10 + H 2 Amyl alcohol. Amylene. 476 ELEMENTS OF MODERN CHEMISTRY. By oxidation, amyl alcohol yields valeric aldehyde and val- eric acid. C 5 H 12 + O = H 2 + C 5 H 10 Valeral, or valeric aldehyde. C 5 H 12 + O 2 = H 2 + C 5 H 10 2 Valeric- acid. The numerous amylic ethers cannot be described here. Amyl oxide, (C 5 H n ) 2 0, is a colorless liquid, having a suave odor, and boiling at 176 (Williamson). Amyl chloride, C 5 H U C1, is a colorless liquid of an aromatic odor, boiling at 102. Amyl iodide, C 5 H U I. is a colorless liquid, which becomes brown when exposed to the light. Density at 0, 1.4676. Boiling-point, 147. Isomerides of Amyl Alcohol. At least five alcohols are known having the composition of amyl alcohol. Independ- ently of the normal alcohol CH 3 -CH 2 -CH 2 -CH 2 -CH 2 .OH (boiling-point, 137), which Lieben obtained by the action of nascent hydrogen on valeral (valeric aldehyde), and the alco- hol of fermentation which has just been described, and which may be called isopropyl-ethyl alcohol, there are three others having the composition C 5 H 12 0. The most important is the compound which is generally called hy- drate of amylene, because it breaks up very readily into water and amylene. It is a tertiary alcohol of the form Its corresponding iodide is formed by direct union of hydri- odic acid and the amylene prepared by the action of zina chloride upon amyl alcohol of fermentation (A. Wurtz). CH 10 -j- HI = C 5 H"I This iodide boils at 129. By treating it with water and silver oxide, Wurtz obtained the alcohol which he named hydrate of amylene. The latter liquid boils at 105. It is decomposed by heat alone into amylene and water, according to the equation before given. The other isomerides of amyl alcohol need not be described. SERIES OF ALCOHOLS. 47*7 Hexyl and Heptyl Alcohols. Faget announced that the residues from the distillation of fusel-oil from fermented grape- juice contained a small quantity of hexyl (C 6 H 14 0) and heptyl (C 7 H 16 0) alcohols, but such alcohols have not been refound in that product. Normal hexyl alcohol has been obtained from the volatile oil of the seeds of Heracleum giganteum,, an oil which contains butyrate of hexyl, C 6 H 13 .C 4 H 7 2 . The normal alcohol boils at 157-158. Normal heptyl alcohol, C 7 H 16 0, has been prepared by the action of nascent hydrogen on oenanthic aldehyde C 7 H 14 0. It boils at 175-17*7, and has an aromatic odor. Octyl Alcohols, C 8 H 18 O. Normal octyl alcohol may be ex- tracted from the seeds of Heracleum spondylium and Hera- cleum giganteum, in which octyl acetate, C 8 H 17 .C 2 H 3 2 , exists. This ether is separated and decomposed by boiling potassium hydrate. Its boiling-point is between 190 and 192. Bouis discovered secondary octyl alcohol. By boiling one of the acids produced by the saponification of castor-oil, rici- nolic acid, with potassium hydrate, Bouis decomposed it into sebacic acid and a new secondary alcohol. This is octyl alco- hol, C 8 H 18 0, a colorless liquid having a pleasant, aromatic odor, and boiling at 178. The following equation explains its formation : = K 2 C 10 H 16 4 + C 8 H 18 -f H 2 Kicinolic acid. Potassium sebate. Octyl hydrate. Cetyl Alcohol. The concrete portion of an oil which fills the cranial sinuses of the sperm-whale is called spermaceti. When properly purified it occurs in beautiful pearly plates, fusible at 49. It is a compound ether of which the nature was recognized by Chevreul in 1823. By submitting it to the action of potassium hydrate, that chemist decomposed it into palmitic acid and a new alcohol which he called ethal, to denote its relations with alcohol and ether. It is now called cetyl alcohol, or cetyl hydrate. Cetyl palmitate. Cetyl hydrate. Potassium palmitate. It belongs to the same homologous series as the preceding alcohols. Alcohols from Wax. The most complex alcohols of the series under consideration were obtained from wax by Brodie. 478 ELEMENTS OF MODERN CHEMISTRY. Ordinary beeswax is a mixture of a fatty acid, C 27 H 54 2 , called cerotic acid (cerin), and a compound ether, the palmitate of myricyl (inyricin). The two bodies are separated by alcohol, which readily dissolves the first, but in which the second is but slightly soluble. By boiling the palmitate of myricyl with potassium hydrate, it breaks up into palmitic acid and hydrate of myricyl, or myricyl alcohol, C^H^O. Chinese wax is a compound ether ; it is cerotate of ceryl, and may be decomposed by caustic potassa into cerotic acid and ceryl hydrate, or ceryl alcohol, C 27 H 56 0. The hydrates of cetyl and ceryl are solid bodies. ALLYL ALCOHOL. C8H5.0H = CH^CH-CH 2 .OH All of the alcohols thus far considered belong to the series C n H 2n+2 0. There are other monatomic alcohols which belong to different series, that is, in which there are different relations between the number of hydrogen atoms and the number of carbon atoms. Among these other alcohols, the most impor- tant is allyl alcohol, or hydrate of allyl, so named because it is closely related to the essential oil of garlic, which is allyl sul- phide. Another natural oil, that of mustard, is sulphocyanate of allyl. C 3 H 5 .OH (C 3 H 5 ) 2 S C 3 H 5 .CNS Allyl hydrate. Allyl sulphide. Allyl sulphocyanate. Hofmann and Cahours prepared allyl hydrate and a great number of its derivatives artificially by the aid of allyl iodide, C 3 H 5 I, which is formed when glycerin is acted upon by iodide of phosphorus, P 2 I* (Berthelot and de Luca). This iodide, whose relations to allyl alcohol are the same as those of ethyl iodide to ordinary alcohol, is a colorless liquid, having a slightly pungent, garlicky odor, and boiling at 101. When heated with mercury and concentrated hydrochloric acid, it yields pure propylene gas (Berthelot). 2C 3 H 5 I + 2HC1 + 4Hg = 2C 3 H 6 -f Hg 2 ! 2 -f Hg 2 Cl 2 Allyl iodide. Propylene. Tollens and Henninger discovered a very simple process for the preparation of allyl alcohol. It consists in heating formic acid, or oxalic acid, from which the former acid is produced, with glycerin to 220. The allyl alcohol which distils is COMPOUND AMMONIAS. 479 washed with a concentrated solution of potassium carbonate, and rectified over lime. In this reaction, a monoformine of glycerin is first produced, and this decomposes at 220 into carbon dioxide, water, and allyl alcohol. fO.CHO C3R5 J OH = CO 2 + H 2 + C 3 H5.0H (OH Monoformine of glycerin. Allyl alcohol. It will be seen that the reaction is really a reduction. Allyl alcohol is a colorless liquid, boiling at 97, and having a pungent, alcoholic odor. It dissolves in all proportions of water. Density at 13, 0.86. Allyl alcohol is an unsaturated compound ; it can fix directly two atoms of hydrogen, chlorine, or bromine, or one molecule of hydrobromic acid, etc. Acrolein, a volatile liquid that is formed in the distillation of fatty bodies, is the aldehyde of allyl alcohol. Acrylic acid is the corresponding acid. COMPOUND AMMONIAS, OR AMINES. Wurtz gave these names to the basic combinations resulting from the substitution of alcoholic radicals, such as methyl, ethyl, etc., for the hydrogen of ammonia. This substitution may be more or less complete ; 1, 2, or 3 atoms of hydrogen may be replaced by as many alcoholic groups. Hence there are various classes of amines ; they are designated by the names primary, secondary, and tertiary. PRIMARY AMINES. SECONDARY AMINES. TERTIARY AMINES. H) CH3) CHn CHM H V N H \ N CH3 [ N CH3 [ N Hj HJ Hj CH3J Ammonia. Methylamine. Dimethylamine. Trimethylamine. C2H5) C2H5) C 2 H5) H [ N C 2 H& I N C 2 H5 I N H j H J C 2 H5 J Ethylatnine. Diethylamine. Triethylamine. Lastly, bases are known which are the most energetic of all, and may be considered as derived from the hypothetical hydrate of ammonium by the substitution of alcoholic radicals for 4 atoms of hydrogen. 480 ELEMENTS OF MODERN CHEMISTRY. } C2H5 ( XT nw C 2 H5 N ' OH C2H5J Hydrate of tetrethylanimoniiim. The latter ammonia-ted bases, as well as the secondary and tertiary amines, were discovered by Hofmann. In the amines, nitrogen acts as a triatomic element or tri- valent; but it may assume two other atomicities. In sal- ammoniac, it is pentatomic, and it may play precisely the same part in the amines. 7 x\ C2R5 C2R5 Triethylaniine. Cl H H *< X N x\ H H AlnmoniTim chloride. (OH)' (C 2 H6)' (C2R5)' <: x N x\ (C 2 H 6 )' (C 2 II 5 )' Tetrethylammonium hydrate. x\ H H Ammonia. Related to the amines are various organic combinations which have the same constitution, but in which the nitrogen is replaced by an analogous element, such as phosphorus, arsenic, or antimony. A great number of these bodies have been discovered, of which the more important are C2H5 ) C 2 H 5 p'" C 2 H 5 L As'" C*H6 \ Sb C2I15 ) C 2 H5 j C 2 II5 J Triethylphosphine. Triethylarsine. Triethylstibine. The nitrogenized bases that have just been considered belong either to the type NX 3 or to the type NX 5 . A new class of compounds has recently been discovered, belonging to the type N 2 X 4 . It is evident that the group NX 2 (amidogen) cannot exist in the free state. If it could be isolated, it would probably combine with itself, forming a double molecule NH 2 Fischer has made known several substituted derivatives of this body, N 2 H 4 , which he names hydrazine. He has described ethylhydrazine, NH 2 -NH(C 2 H 5 ). It is a base soluble in water, and having an ammoniacal odor ; its hydrochloride con- tains N 2 H 3 (C 2 H 5 ).2HC1. The compound ammonias cannot all be described here ; we need only consider the more important. METHYLAMINE. 481 METHYLAMINE. CH3) CH^N =r H [ N HJ This body may be prepared by boiling together potassium hydrate and methyl cyariate or cyanurate, and passing the vapors which are disengaged into dilute hydrochloric acid ; methylauiine hydrochloride is thus formed. PfK CR3 2KOH = K2C 3 Methyl cyanate. Methyl amine. The solution is evaporated to dryness, and the residue fused and allowed to cool ; it is then mixed with double its weight of powdered quick-lime, and the mixture gently heated. The methylamine disengaged may be collected over mercury. It is a colorless gas, which condenses to a light liquid at a temperature a few degrees below 0. It is inflammable, and burns with a pale flame. Its odor is strongly ammoniacal and, at the same time, recalls that of the sea. It is the most solu- ble of all gases. 1 volume of water at 12.5 absorbs 1153 volumes of methylamine. The aqueous solution possesses the odor of the gas, a caustic taste, and a strong, alkaline reaction. Like ammonia, it precipitates the oxides from solutions of the metallic salts. If a solution of methylamine be added to a solution of cupric sulphate, a light-blue precipitate is first formed, but disappears if an excess of methylamine be added, yielding a beautiful blue solution. Methylamine Hydrochloride, CH 5 N.HC1, differs from am- monium chloride by its solubility in boiling alcohol, from which it is deposited on cooling in large, colorless, deliquescent plates. With platinic chloride it forms a yellow precipitate, soluble in boiling water, from which it crystallizes in golden-yellow scales. It is a chloroplatinate, (CH 5 N.HCl) 2 .PtCl 4 . DIMETHYLAMINE, TRIMETHYLAMINE, TETRA- METHYLAMMONIUM HYDRATE. These compounds were discovered by Hofmann. Dimethylamine, (CH 3 ) 2 NII, is a combustible gas which lique- fies at 8. v 41 482 ELEMENTS OF MODERN CHEMISTRY. Trimethylamine, (CH 3 ) 3 N, exists ready formed in the CTieno- podium vulvaria^ in the flowers of Cratsegus oxyacantha, in herring-brine, in cod-liver oil, and in coal-gas tar. Vincent extracts large quatities of it from the residues of the distilla- tion of fermented beet-juice. At ordinary temperatures it is a gas; it liquefies at 9. It is very soluble in water and in alcohol. It has a strong, ammoniacal odor, and an intense, alkaline reaction. It unites directly with methyl iodide, forming the iodide of tetramethylanimonium. (CH 3 /N + CtPI = (CH 3 /NI This iodide possesses all the appearances of a salt. It is soluble in water, and the solution treated with silver oxide yields silver iodide and tetramethylanimonium hydrate. 2(CH 3 ) 4 NI -f Ag 2 + H 2 = 2AgI + 2(CH 3 ) 4 N.OH The latter body is very soluble in water, and the solution is caustic. When submitted to dry distillation, it decomposes into trimethylamine and methyl alcohol. (CH 3 ) 4 N.OH = CH 3 .OH + (CH 3 ) 3 N ETHYLAMINE. C 2 H'N = H \ N HJ Ethylamine is prepared by a process analogous to that which yields methylamine ; cyanate or cyanurate of ethyl is decom- posed with boiling potassium hydrate, and the vapors are con- densed in very dilute hydrochloric acid. The dry ethylamine hydrochloride is then treated with quick-lime (A. Wurtz). Another process has been indicated by Hofmann. It consists in causing ammonia to react upon the bromide or iodide of ethyl. H) eras} C2H&Br + H \ N = H > N.HBr HJ HJ Ethylamine hydrobromide. Ethylamine is a light, mobile, colorless liquid; it boils at 18.7. Its odor is strong and exactly resembles that of am- monia. Ethylamine is inflammable. It mixes with water, alcohol, and ether in all proportions. Its aqueous solution is caustic, and precipitates most of the metallic salts like solution of am- ETHYLPHOSPHINES. 483 monia, and, like the latter, redissolves cupric hydrate, forming a blue liquid. Ethylamine Hydrochloride, C 2 H Y N.HC1. This salt crys- tallizes in large, deliquescent plates, soluble in absolute alcohol. Its aqueous solution yields with platinic chloride a precipitate composed of yellow scales, soluble in boiling water, and consti- tuting a chloro-platinate, (C 2 H 7 N.HCl) 2 .PtCl 4 . DIETHYLAMINE, TRIETHYLAMINE, TETRETHYL- AMMONIUM HYDRATE. C 2 H 5 ^ Diethylamine, C 2 H 5 v N, was obtained by Hofmann by heat- H ) ing ethylamine with ethylbromide, and decomposing the die- thylamine hydrobromide formed by an alkali. N.HBr H H Ethylamine. Diethylamine hydrobromide. The free base is a liquid having an ammoniacal odor and boiling at 57.5 Triethylamine may be formed by the action of ethyl bro- mide on diethylamine ; triethylamine hydrobromide is formed, C 2 H 5 >- N.HBr, from which alkalies cause the disengagement C 2 H 5 ) of triethylamine, a colorless liquid, boiling at 91 ; its odor is ammoniacal and its reaction strongly alkaline. Tetrethylammonium Hydrate. When a mixture of ethyl iodide and triethylamine is heated on a water-bath, the two bodies combine, forming the compound which Hofmann has named tetrethylammonium iodide. C 2 H 5 I + (C 2 H 5 ) 3 N = (C 2 H 5 ) 4 N.I Ethyl iodide. Triethylamine. Tetrethylammonium iodide. When this is treated with silver oxide and water, it yields silver iodide and tetrethylammonium hydrate, (C 2 H 5 ) 4 N.OH, a powerful base, which is crystallizable and soluble in water. Its energy is comparable to that of potassium hydrate. ETHYLPHOSPHINES. Primary, secondary, and tertiary ethylphosphines are known, as well as the compounds of tetrethylphosphonium. 484 ELEMENTS OF MODERN CHEMISTRY. H | P'" C 2 H5 P'" C 2 H 5 P'" p 25 P- H J HJ Ethylphosphine. Diethylphosphine. Triethylphosphine. Tetrethylphosphonium. (Primary.) (Secondary.) (Tertiary.) The first two have been recently discovered by Hofmann. The third is due to an admirable research of Hofmann and Cahours, who obtained it by the action of phosphorus trichloride on zinc ethyl. 2PC1 3 + 3[Zn(C 2 H 5 ) 2 ] = 2[P(C 2 H 5 ) 3 ] -f SZnCl 2 Zinc ethyl. Trietbylphosphine. The operation must be conducted out of contact with the air, and the zinc ethyl must be diluted with anhydrous ether. Monethylphosphine and diethylphosphine are produced when ethyl iodide is made to react upon phosphonium iodide, PH*I, hydriodide of hydrogen phosphide (page 167), in presence of an excess of zinc oxide. 2PH*I + ZnO = 2[(C 2 H5)H 2 P.HI] + Znl 2 + H 2 2C 2 1M + PH*I + ZnO == (C 2 H5) 2 HP.HI + Znl 2 + H 2 As both reactions are accomplished simultaneously, both phosphines are obtained at the same time. They are separated by the action of water upon the two hydriodides which are formed. That of monethylphosphine is decomposed by water, while that of diethylphosphine is only decomposed by the alka- lies. It is sufficient then to add water to the product of the reaction in order to set free the monethylphosphine ; when the latter has been completely expelled by heat, potassium hy- drate added to the residue will cause the disengagement of the diethylphosphine. These operations should be conducted in a current of hydrogen. Monethylphosphine, (C 2 H 5 )H 2 P. This is a colorless liquid, lighter than water, in which it is insoluble, and boiling at 25. It has a most disagreeable odor. It takes fire on contact with chlorine or nitric acid. Its hydriodide crystallizes in beautiful, white, quadrangular tables. Diethylphosphine, (C 2 H 5 ) 2 HP. A colorless liquid, lighter than water, and boiling at 85. It is very avid of oxygen, and sometimes takes fire spontaneously on contact with the air. Triethylphosphine, (C 2 H 5 ) 3 P. This is a colorless liquid, boiling at 127.5. Density at 15, 0.812. It combines di- rectly with oxygen, forming triethylphosphine oxide, (C 2 H 5 ) 3 PO. The latter is a crystalline solid, very soluble in water and in alcohol. It distils at 240. PRODUCTS OF OXIDATION OF ETHYLPHOSPHINES. 485 When treated with ethyl iodide, triethylphosphine yields tetrethylphosphonium iodide, (C 2 H 5 )*PI, a compound which may be obtained in beautiful crystals. When this iodide is acted upon by moist silver oxide, it furnishes the corresponding hydrate, which is an energetic base. 2[(C 2 H 5 )TI] + Ag'O + H 2 = 2AgI + 2[(C 2 H 5 ) 4 P.OH] Tetrethylphosphonium Tetrethylphosphonium iodide. hydrate. PRODUCTS OF OXIDATION OF ETHYLPHOS- PHINES. When the ethylphosphines are treated with fuming nitric acid under suitable conditions, they act in a characteristic man- ner. Monethylphosphine is transformed into a dibasic acid, monethylphosphinic j diethylphosphine yields a monobasic acid, diethylphosphinic. Triethylphosphine yields an indifferent oxide, which has already been mentioned. Now, if it be remem- bered that under the same circumstances hydrogen phosphide furnishes phosphoric acid, it will be seen that the preceding oxidation compounds may be regarded as phosphoric acid, in which 1, 2, or 3 groups OH ,are replaced by as many ethyl groups. C H H (H (OH PO^ OH I OH Hydrogen phosphide. Phosphoric acid. ( C 2 H* f CH& P^H PO^OH (H (OH Monethylphosphine. Monethylphosphinic acid. f C 2 H& P \ C 2 H 5 PO (H (OH Diethylphosphine. Diethylphospliinic acid. ( C 2 H5 f P C 2 H 5 PO Triethylphosphine. Triethylphosphine oxide. The compounds of arsenic and ethyl are entirely analogous to the phosphines ; they have already been alluded to. Besides these, there are ethylic combinations corresponding to cacodyl and its derivatives. 41* 486 ELEMENTS OF MODERN CHEMISTRY. ORQANO-METALLIC COMPOUNDS. ZINC-ETHYL. Zn // (C 2 H 5 ) 2 One of the more important of the compounds formed by the union of the metals with alcoholic radicals is zinc-ethyl, dis- covered by Frankland. It is prepared by heating ethyl iodide with zinc-turnings and a small quantity of sodium on a water-bath. Zinc iodide and zinc-ethyl are formed. When the reaction is terminated, the product is distilled and that portion collected which passes above 115. Zinc-ethyl is a colorless, mobile, and highly-refractive liquid. It has a peculiar, penetrating, and very disagreeable odor. It boils at 118. It takes fire spontaneously on contact with the air, burning with a green flame, and producing white fumes of zinc oxide. If water be added to a small quantity of zinc-ethyl contained in a tube, a brisk effervescence at once takes place, and a white deposit is formed. The gas is ethane, and the deposit is zinc hydrate. Zn(C 2 H 5 ) 2 + 2H 2 == Zn(OH) 2 + 2C 2 H 6 Zinc-ethyl will enter into double decompositions. By the action of phosphorus trichloride on this body, Hof- mann and Cahours obtained triethylphosphine and zinc chloride. There is a zinc-methyl, Zn(CH 3 ) 2 , corresponding to zinc- ethyl. MERCUR-METHYL AND MERCUR-ETHYL. These compounds were obtained by Frankland and Duppa, by the action of methyl and ethyl iodides on sodium amalgam (sodium 1, mercury 500), in presence of a small quantity of acetic ether. Mercur-ethyl is a colorless, inflammable liquid, insoluble in water. Density, 2.44. Boiling-point, 158-160. It is one of the most dangerous bodies known. The inhalation of its vapor for any length of time, even in small quantity, will produce fatal poisoning. STANNETHYLS. 487 Chlorine, bromine, and iodine instantly decompose mercur- ethyl with formation of a compound of mercur-monethyl. f P2TT5 ( P2rr5 TT 3 ^ ** I T2 P 2 R5T I TTo- J Hg < Q 2 jj5 -j- 1 Hg I j Mercur-ethyl. Ethyl iodide. Mercur-monetliyl iodide. STANNETHYLS. The discovery of the numerous compounds of tin and ethyl is due to Lbwig. Their history has been completed by Frank- land, Cahours, and Hiche. As the nomenclature and constitution of the stannethyls have already been indicated (page 424), we need only consider a few of these interesting compounds. Stannodiethyl, Sn(C 2 H 5 ) 2 . The iodide of this compound is obtained when ethyl iodide is heated with tin-filings to about 180. This iodide, Sn(C 2 H 5 ) 2 ! 2 , purified by crystallization in alcohol, furnishes free Stannodiethyl when its solution is treated with zinc, which removes the iodine. Stannodiethyl is an oily, yellow liquid, which does not vola- tilize without decomposition. When heated to 150 it begins to boil, but the greater part of it is decomposed into stanno- tetrethyl and tin. 2[Sn(C 2 H 5 ) 2 ] = Sn(C 2 H 5 ) 4 + Sn The iodide of Stannodiethyl crystallizes in pale yellow needles. In its solution, the alkalies precipitate the oxide Sn(C 2 H 5 ) 2 0, which forms an amorphous, white precipitate, insoluble in water and alcohol, but soluble in the alkalies and acids with which it forms salts. Stannotriethyl or Sesquistannethyl, Sn 2 (C 2 H 5 ) 6 = (C 2 H 5 ) 3 Sn-Sn(C 2 H 3 ) 3 . This is formed, together with the preceding compound, by the reaction of ethyl iodide on an alloy of tin and sodium. It is separated by fractional distillation ; it boils between 265 and 270. It plays the part of a radical and combines directly with oxygen. The oxide contains Sn 2 (C 2 H 5 ) 6 = [Sn(C 2 H 3 ) 3 ] 2 0. It combines with the elements of water, form- ing a hydrate, Sn(C 2 H 5 ) 3 .OH, crystallizable in prisms. These crystals are fusible at 44. The oxide distils at 272. It reacts with the acids to form crystallizable salts. [Sn(C 2 H 5 ) 3 ] 2 + 2HN0 3 = 2[Sn(C 2 H 5 ) 3 .N0 3 ] -f- H 2 Stan notrietliyl oxide. Stannotriethyl nitrate. 488 ELEMENTS OF MODERN CHEMISTRY. The iodide, Sn(C 2 H 5 ) 3 I, is a liquid having a mustard-like odor, and distilling without decomposition towards 235-238. Density at 15, 1.833. Stannotetrethyl, Sn(C 2 H 5 ) 4 . Colorless liquid, almost odor- less, and boiling at 181. Density, 1.187. It is formed by the action of zinc ethyl on stannodiethyl iodide. Sn(C 2 H 5 ) 2 ! 2 -f Zn(C 2 H 5 ) 2 = Sn(C 2 H 5 ) 4 -f ZnP Stannnodiethyl iodide. Zinc-ethyl. Stannotetretbyl. It is a saturated compound, and does not enter into combi- nation, but by the action of energetic reagents it yields com- pounds of stannodiethyl or stannotriethyl. Thus, with iodine, the following reaction takes place : Sn(C 2 H 5 ) 4 + P = Sn(C 2 H 5 ) 3 I -f C 2 H 5 I VOLATILE FATTY ACIDS DERIVED FROM THE ALCOHOLS. Modes of Formation and Constitution. These acids result from the oxidation of the alcohols of which the principal com- pounds have been described. They are formed in a great num- ber of reactions, and many of them exist already formed in nature, either in the free state or in combination in neutral fatty compounds, that is, the oils and fats. Their composition is expressed by the general formula C n H 2n O 2 ; they contain one more atom of oxygen and two atoms of hydrogen less than their corresponding alcohols. Their principal modes of formation are as follows : 1. By oxidation of an alcohol : CH 4 -j- O 2 = CH 2 2 4- H 2 Methyl alcohol. Formic acid. 2. By oxidation of an aldehyde : C 2 H 4 + = C 2 H*0 2 Aldehyde. Acetic acid. 3. By the decomposition of an organic cyanide with boiling potassium hydrate: CH 3 OH 3 + KOH + H!O = Methyl cyanide. Potassium acetate. VOLATILE FATTY ACIDS. 489 The acetic acid is formed in this last reaction, by the union of the carbon of the cyanogen group with the oxygen of both the potassium hydrate and the water, the hydrogen of these two bodies combining with the nitrogen of the cyanogen to form ammonia. It may then be admitted that acetic acid con- tains a radical carbonyl, CO, united on the one hand with a methyl group (that of the methyl cyanide), and on the other with a hydroxyl group, OH. The other acids of the series possess an analogous constitu- tion. CH 3 C 2 H5 C 3 H 7 C 4 H CO.OH CO.OH CO.OH CO.OH etc. Acetic acid. Propiouic acid. Butyric acid. Valeric acid. 4. A method of synthesis, discovered by Wanklyn, furnishes a direct support to this theory of the constitution of the fatty acids. That chemist realized the synthesis of acetic and pro- pionic acids by passing a current of carbonic acid gas over sodium-methyl and sodium-ethyl, organo-metallic compounds which result from the action of sodium upon zinc-methyl and zinc-ethyl. OTT3 NaCH + CO.O = f CO.ONa Sodium-methyl. Sodium acetate. CO.O CO.ONa Sodium-ethyl. Sodium propionate. General Properties. 1. The volatile fatty acids of the series C n H 2n 2 are monobasic ; each contains one atom of hydrogen which may be replaced by an equivalent quantity of a metal. 2. When submitted to dry distillation, many of their salts yield an acetone and a carbonate. CH = CO + CaC03 CH 3 Calcium acetate. Acetone. Calcium carbonate. 3. The same reaction may produce an aldehyde and a hydro- carbon of the series C n H 2n (Chancel). C 3 H 7 Calcium butyrate. Butyral, or butyric Propylene. aldehyde. V* 490 ELEMENTS OP MODERN CHEMISTRY. 4. When a mixture of a salt of a fatty acid and a formate is subjected to dry distillation, the principal product of the reaction is an aldehyde (Piria). CH 3 CH3-CO.OK + H-CO.OK = i + KXIO 3 CHO Potassium acetate. Potassium formate. Aldehyde. 5. The fatty acids are converted into chlorides by the action of phosphorus pentachloride, or oxy chloride (Grerhardt). C2H300K + PGP = C 2 H 3 O.C1 + POC1 3 + KC1 Potassium acetate. Acetyl chloride. Phosphorus oxychloride. 6. By the action of these chlorides upon the salts of the fatty acids, the anhydrides of the acids are formed (Gerhardt). C H3 }0 + CTF.OC1 =, KC. + Potassium acetate. Acetyl chloride. Acetic anhydride. 7. When subjected to the action of phosphoric anhydride, the ammonium salts of these acids lose 2H 2 and are con- verted into nitriles or cyanogen ethers (Dumas, Malaguti and Le Blanc, Frankland and Kolbe). CH 3 CH 3 _L- CO.O(NH 4 ) CN Ammonium acetate. Acetonitrile. (Methyl cyanide.) FORMIC ACID. CH'O 2 This acid, which was discovered by S. Fischer in 1760, in red ants, is formed in a great number of reactions, particularly in the oxidation of methyl alcohol, in the decomposition of hydrocyanic acid by acids or alkalies, in the distillation of oxalic acid, and in the oxidation of many organic matters, such as starch, sugar, etc. Berthelot achieved its direct synthesis by heating carbon monoxide for a long time to 100 in sealed flasks containing a concentrated solution of potassium hydrate. CO + KOH = HCO.OK Potassium formate. Preparation. Starch, manganese dioxide, and dilute sul- phuric acid may be boiled together in a capacious retort, and the acid liquid which condenses in the receiver saturated with lead carbonate. Lead formate is thus obtained, and is purified FORMIC ACID. 491 by crystallization. To obtain formic acid, the salt is heated in a current of dry hydrogen sulphide. Formic acid distils (Db'bereiner). Another and better process consists in heating to 100 equal parts of oxalic acid and glycerin. Under these conditions, the oxalic acid breaks up into carbonic acid gas, and formic acid which distils. The liquid is saturated with lead carbonate, and the preparation concluded as before (Berthelot). Properties. Formic acid is a colorless liquid, having a pungent odor and a very acid taste. It boils at 99, and solid- ities to a crystalline mass at 8.5. It mixes with water in all proportions. If an excess of sulphuric acid be added to a small quantity of formic acid contained in a test-tube, and a gentle heat be applied, a regular disengagement of gas will take place ; it may be ignited at the mouth of the tube, and will burn with a blue flame. It is carbon monoxide, and is formed according to the fol- lowing equation : CH 2 2 = CO + H 2 If formic acid be added to a solution of silver nitrate, and the liquid be heated, it will soon become clouded ; silver will be precipitated as a gray powder, and carbon dioxide will be disengaged. The formic acid becomes oxidized in reducing the silver nitrate, CH 2 2 + = CO 2 + H 2 Chlorine determines an analogous decomposition. CH 2 2 + Cl 2 == CO 2 + 2HC1 Formates. Formic acid is an energetic acid, perfectly neu- tralizing the bases. It is monobasic; one of its hydrogen atoms can be replaced by an equivalent quantity of metal. The formates are soluble ; the most characteristic are cupric for- mate, Cu(CH0 2 ) 2 -f- 4H 2 O, which crystallizes in magnificent, oblique rhombic prisms, and lead formate, Pb(CH0 2 / 2 , which forms long, colorless needles, slightly soluble in cold water. Ammonium formate, which is obtained by saturating formic acid with ammonia, crystallizes in prisms which are very solu- ble in water. When quickly heated to about 200, it breaks up into hydrocyanic acid (formonitrile) and water (Pelouze). (NIP)CHO 2 = 2H 2 + CNH 492 ELEMENTS OF MODERN CHEMISTRY. FORMIC ALDEHYDE. CH*0 = H-CHO Hofmann has recently obtained this body by the slow com- bustion of methyl alcohol, brought about by a spiral of platinum wire. CH 4 + O = H 2 + CH 2 It is also formed in the distillation of barium and calcium formates. It is not known in the pure state. It has a great tendency to become polymerized, forming a solid compound, which Boutlerow has named trioxymethylene, and which prob- ably contains C 3 H 6 3 . ACETIC COMBINATIONS. It may be admitted that these compounds contain the mon- atomic radical acetyl (C 2 H0 3 / = (CH 3 -CO)', which may be regarded as oxidized ethyl. CH 3 Ethyl. Acetyl. Aldehyde is the hydride of this radical ; acetic acid is its hydrate, and acetone its methylide. Besides these, there are known the oxide and chloride of acetyl, an acetyl ammonia, which is acetamide, etc. The following formulae indicate the relations between all of these bodies : C 2 H 3 O.H C 2 H 3 .OH Acetyl hydride (aldehyde). Acetyl hydrate (acetic acid). C 2 H 3 O.C1 (C 2 II 3 0) 2 Acetyl chloride. Acetyl oxide (acetic anhydride). C 2 H 3 C 2 H 3 O.CH 3 H N Acetyl methylide (acetone). Acetamide. ACETIC ACID. C 2 H<0 2 Acetic acid is the acid of vinegar. It is the product of the oxidation of alcohol. It is formed in a number of other reac- tions, among which we may mention the oxidation of aldehyde, ACETIC ACID. 493 the decomposition of methyl cyanide by potassium hydrate, the action of carbon dioxide on sodium-methyl, and the dry distil- lation of a great number of organic substances, such as wood, starch, gum, sugar, etc. Preparation. The large quantities of acetic acid employed in the arts are obtained by the destructive distillation of wood. The operation is conducted in large iron cylinders, heated directly by a fire (Fig. 123). The products of the distillation consist of liquids and gases. The liquids are condensed in a large worm, , cooled by a continual circulation of cold water through surrounding pipes mm ; the gases are conducted back to the fire-grate by the pipe h. The condensed product consists of an aqueous portion and of tar. The greater part of the latter is separated by a new distillation ; the first portions which pass contain wood-spirit, after which acetic acid distils. The acid liquid is neutralized by lime, and the calcium ace- tate formed is converted into sodium acetate by adding a solu- tion of sodium sulphate. The liquid, separated by filtration from the calcium sulphate, yields on evaporation sodium ace- tate, still colored brown by tarry matters. The latter are destroyed by frying the salt, that is, by heating it for some time to 250, a temperature which carbonizes the tar but does not affect the sodium acetate. The mass is then exhausted with water, the solution filtered, concentrated, and crystallized. Crystals of pure sodium acetate are thus obtained, a salt which was formerly called pyrolignite of soda. Acetic acid is pre- 42 494 ELEMENTS OF MODERN CHEMISTRY. pared by drying this salt and distilling it with J its weight of concentrated sulphuric acid. Or the dry salt may be decomposed by an exact quantity of sulphuric acid. The acetic acid which separates from the sodium sulphate may then be decanted, and cooled in a freez- ing mixture. The portion remaining liquid is separated and the solid mass constitutes pure acetic acid. Vinegar. Vinegar is the product of the acid fermentation of wine and other alcoholic liquids. The following process is largely employed for the conversion of wine into vinegar. It is the Orleans process. A small quantity of warm vinegar is first introduced into large vats, which have already been used for the operation and are impregnated with the peculiar fer- ment formed ; quantities of wine are then added at intervals of several days, the vats being maintained at a temperature between 24 and 27. In a fortnight, the acetification is com- plete, and a portion of the vinegar is withdrawn and replaced by a new quantity of wine which also becomes converted into vinegar. The process is thus continuous. Under these cir- cumstances, the alcohol is converted into acetic acid by the influence of a peculiar ferment that is called mother of vinegar. It is a vegetable product, a mycoderm ( Mycoderrna aceti), which appears on the surface of the liquid, where it absorbs oxygen from the air and subse- quently cedes it to the alcohol (Pasteur). Its action may be compared to that of platinum black. By another process, a mixture of weak alcohol, water, and albuminoid matter (the juice of pota- toes, beets, etc.), contain- ing the elements neces- sary for the production of the ferment, is allowed to trickle over beech-wood shavings. The latter, which have been previously steeped in strong "vinegar, are contained in a large cask, A (Fig. 124), FIG. 124. ACETATES. 495 where they rest upon a double bottom perforated with holes. Tubes, ttj pass through the upper portion, maintaining a current of air which enters at the lower portion of the cask. Under these conditions, the liquid, which spreads over the shavings and exposes a considerable surface to the air, becomes oxidized with such energy that the temperature soon rises to 30 ; a second passage of the liquid through the casks completes the acetification. Properties of Acetic Acid. Acetic acid is solid below 1*7, and crystallizes in large plates. It boils at 118. Its density at is 1.0801. Its odor is pungent and acid. It is very corrosive. It mixes with water and alcohol in all proportions, and when it is added to water there is a contraction in volume. The maximum contraction, and consequently the maximum density of aqueous acetic acid, corresponds to a mixture con- taining C 2 H 4 2 -f H 2 0. Vapor of acetic acid passed through an incandescent porce- lain tube yields gases and deposits carbon, at the same time forming small quantities of acetone, benzol, phenol, and naph- thaline (Berthelot). Phosphorus pentachloride converts acetic acid into acetyl chloride, with formation of hydrochloric acid and phosphorus oxychloride. C 2 H 3 O.OH + PCP = C 2 H 3 O.C1 + HC1 + POC1 3 Acetic acid. Acetyl chloride. If a mixture of small quantities of potassium acetate and arsenious oxide be heated in a test-tube, dense white vapors having an intense and disagreeable odor of garlic will be dis- engaged. This experiment permits the detection of minute traces of acetic acid ; if the latter exist in the free state in the liquid, its potassium compound must first be formed. The white vapor disengaged is due to a body formerly known as fuming liquor of Cadet (see page 453). ACETATES. The more important neutral acetates have the composition R'(C 2 H 3 2 ) or R"(C 2 H 3 2 ) 2 , according as the metal which replaces the basic hydrogen of the acetic acid is univalent or bivalent. There are many basic acetates. Potassium Acetate, KC 2 H 3 2 . This is prepared by satu- 496 ELEMENTS OF MODERN CHEMISTRY. rating acetic acid with potassium carbonate and evaporating to dryness. It is thus obtained in crystalline, very deliquescent laminae. It melts at 292, and is very soluble in water. Sodium Acetate, NaC 2 H 3 O 2 -f 3H 2 0. This salt is obtained on a large scale in the arts in the manufacture of acetic acid. It was formerly called pyrolignite of soda. It crystallizes in large, oblique rhombic prisms, which are very soluble in water, and effloresce in dry air. Acetates of Lead. Neutral lead acetate, Pb(C 2 H 3 2 ) 2 -f 3H 2 0, known also as sugar of lead, is made by neutralizing acetic acid with litharge. It crystallizes in transparent, efflor- escent, oblique rhombic prisms, having a sweet and astringent taste. It dissolves in half its weight of cold water, and in 8 parts of alcohol. It melts in its water of crystallization at 75.5. The neutral solution of lead acetate dissolves oxide of lead, forming different basic salts, according to the proportion of oxide dissolved. The more important of these are a dibasic acetate, Pb(C 2 H 3 2 ) 2 -f PbO -f 4H 2 0, and a tribasic acetate, Pb(C 3 H 3 2 ) 2 -f 2PbO -f nH 2 0. These two salts are gener- ally formed simultaneously when a solution of lead acetate is boiled with litharge. The solution thus obtained is used in medicine as Goulard's solution. If a few drops of it be added to ordinary river or well water, a cloud is produced, owing to the formation of lead sulphate and carbonate. If carbonic acid gas be passed into a solution of the sub- acetate of lead, a deposit of lead carbonate is formed. In this reaction, which serves for the preparation of white lead by the Clichy method, the excess of lead is removed from the subace- tate by the carbonic acid, neutral acetate being formed and remaining in solution, Acetates of Copper. The neutral acetate Cu(C 2 H 3 2 ) 2 + IPO, is prepared by double decomposition by mixing hot solu- tions of sodium acetate and cupric sulphate. The cupric acetate is deposited on cooling in beautiful, oblique rhombic prisms of a deep bluish-green color. They dissolve in 5 times their weight of boiling water. The dilute aqueous solution is de- composed by boiling, a tribasic acetate being formed, while acetic acid is set free. When cupric acetate is heated, it first loses its water of crys- tallization, and decomposes when the temperature reaches 240 or 250, disengaging acetic acid, acetone, and carbon dioxide. ETHYL ACETATE. 497 The residue is finely-divided copper. The product of the dis- tillation is a blue liquid, which, when rectified, yields colorless acetic acid mixed with a small quantity of acetone. It was formerly called radical vinegar. The name verdigris is applied to a basic acetate of copper consisting mostly of a dibasic acetate, Cu(C 2 H 3 2 ) 2 -f- CuO -f- 6 IPO. Verdigris is prepared by exposing to the air copper sheets piled up in layers with the pulp of grapes. In a few weeks the metal becomes covered with bluish crusts of verdi- gris, which are scraped off and delivered to commerce in the form of light-blue balls. The alcohol, formed by the fermenta- tion of the sugar contained in the grape-pulp, becomes oxidized by the air and is converted into acetic acid, and under the in- fluence of the latter, the copper itself absorbs oxygen. Water and copper basic acetate are thus formed. Silver Acetate, AgC 2 H 3 2 . This salt, which is but slightly soluble in water, is precipitated when concentrated solutions of sodium acetate and silver nitrate are mixed. It is deposited from boiling water in brilliant, pearly, flexible plates, which darken on exposure to light. Ammonium Acetate, (NH*)C 2 H 3 2 . When acetic acid is saturated by a current of ammonia gas, this salt is obtained as a deliquescent, crystalline mass. It is very soluble in water and in alcohol. When heated, it first loses ammonia, then acetic acid, and acetamide finally distils. NH 4 .C 2 H 3 2 = H 2 + C 2 H 3 O.NH 2 Ammonium acetate. Acetamide. It is used in medicine under the name spirit of Mindererus. This is generally an impure solution of ammonium acetate, charged with empyreumatic matters. When distilled with phosphoric anhydride, ammonium ace- tate yields methyl cyanide, or acetonitrile. NH*.C 2 H 3 2 = C 2 H 3 N + 2H 2 ETHYL ACETATE. This acetate, ordinarily known as acetic ether, is prepared by distilling a mixture of alcohol, sulphuric acid, and potassium or sodium acetate. The ethyl acetate passes over, together with a certain quantity of alcohol which escapes the reaction. 42* 498 ELEMENTS OP MODERN CHEMISTRY. It is purified by agitation with a solution of calcium chloride, and the ether which floats is decanted, dried over calcium chloride, and rectified on the water-bath. It is a colorless liquid having a very agreeable, ethereal odor. It boils at 77. Density at 0, 0.9105. It is but slightly soluble in water, but dissolves in all proportions in alcohol and ether. Like all compound ethers, it is readily decomposed by potassium hydrate. C 2 H 5 .C 2 IF0 2 + KOH = KC 2 IP0 2 + CTP.OH Ammonia converts it into acetamide and alcohol. C 2 H 3 O.OC 2 H 5 + NH 3 = C 2 H 5 .OH -f C 2 H 3 O.NH 2 Ethyl acetate undergoes a remarkable reaction with sodium. The metal dissolves in the ether, forming sodium ethylate and the compound C 6 H 9 NaO 3 . 2[C 2 H 3 O.OC 2 H 5 ] -f Na 2 = NaO.C 2 H 5 + C 6 H 9 Na0 3 -f H 2 The body C 6 IPNa0 3 is the sodium compound of acetyl-acetic ether, C 6 H 10 3 == C 2 H 2 (C 2 HWO-OC 2 H 5 , which is derived from acetic ether, C 2 H 3 0-OC 2 H 5 , by the substitution of an acetyl group, C 2 H 3 0, for one atom of hydrogen in the radical acetyl. The free acetyl-acetic ether may be obtained by the action of hydrochloric acid upon the sodic compound C 6 H 9 Na0 3 . It is a colorless liquid having an agreeable odor, and boiling at 182. Density at 5, 1.03. SUBSTITUTION PRODUCTS OF ACETIC ACID. Three chlorinated acids are known which are derived from acetic acid by substitution : Monochloracetic acid C 2 H 3 C10 2 Dichloracetic acid C*H*C1 2 Trichloracotic acid C 2 HC1 3 2 Monochloracetic acid is formed when a current of chlorine is passed into acetic acid heated to 100, and containing a small quantity of iodine. As soon as chlorine begins to be disen- gaged at the extremity of the apparatus, the operation is arrested and the liquid distilled. That portion is collected which passes between 185 and 187. Monochloracetic acid is solid, and crystallizes in deliquescent, rhomboidal tables or in prisms. It boils between 185 and 187.8. ACETIC ANHYDRIDE. 499 It is very corrosive. It is converted into glycollic acid when heated with an excess of potassium hydrate. KC 2 H 2 C10 2 + KOH = KC 2 H 2 (OH)0 2 + KC1 Potassium Potassium glycollate. monochloracetate. Ammonia converts it into acetamic or amidacetic acid C 2 H 2 (NH 2 )O.OH (glycocol) (Cahours). + NH3 - HCl + CO.OH CO.OH Monochloracetic acid. Glycocol. Trichloracetic acid, C 2 HC1 3 2 , a very important compound in the history of the science, was discovered by Dumas in 1840. It was then one of the most remarkable examples of a body formed by substitution, and a comparison of its properties with those of acetic acid led Dumas to announce the first idea of chemical types. It is obtained by exposing acetic acid to the action of a large excess of chlorine in direct sunlight. Trichloracetic acid is solid. It forms transparent and deli- quescent, rhombohedral crystals, fusible at 52.3, and boiling between 195 and 200. Its aqueous solution regenerates acetic acid by the action of sodium amalgam, an interesting reaction, since it furnished one of the first examples of inverse substitution (Melsens), as the replacement of chlorine by hydrogen is called. Water and sodium amalgam constitute a slow source of hydrogen. When boiled with potassium hydrate, trichloracetic acid fur- nishes potassium carbonate and chloroform. C 2 HCP0 2 = CHC1 3 + CO 2 ACETIC ANHYDRIDE. This important body, discovered by Gerhardt in 1852, is prepared by the action of one part of phosphorus oxychloride on three parts of dry sodium acetate. In this operation, acetyl chloride is first formed, and this reacts upon an excess of so- dium acetate, producing sodium chloride and acetyl acetate, or acetic anhydride. CTPO.C1 + NO = NaCl + Acetyl chloride. Sodium acetate. Acetic anhydride. 500 ELEMENTS OF MODERN CHEMISTRY. Acetic anhydride is a colorless, mobile liquid, having a strong odor of acetic acid. It boils at 138. When thrown into water, it first sinks to the bottom, and then, absorbing one mol- ecule of water, is converted into acetic acid, which dissolves. ALDEHYDE, OK HYDRIDE OF ACETYL. C 2 H*O This body was discovered by Dbbereiner in 1821 ; its com- position and principal properties were studied by Liebig. Preparation. Aldehyde is prepared by oxidizing alcohol by heating it with manganese dioxide and dilute sulphuric acid, or better, with potassium dichromate and sulphuric acid. The vapors disengaged are condensed in a well-cooled receiver. The distilled liquid is rectified over calcium chloride, only the more volatile portion being collected. This is mixed with twice its volume of ether, and the ethereal solution saturated with ammonia gas. Crystals are deposited which constitute a com- bination of aldehyde with ammonia, and the aldehyde is ob- tained from them by adding a quantity of sulphuric acid exactly sufficient to form ammonium sulphate with the ammonia; a gentle heat is applied, and the aldehyde vapor is passed through a tube filled with calcium chloride, and finally condensed in a well-cooled receiver (Liebig). Properties. Aldehyde is a colorless, very mobile liquid, having a penetrating and somewhat suffocating odor. It boils at 21. It mixes in all proportions with water, alcohol, and ether. It combines with ammonia, forming aldehyde-ammonia, or acetylide of ammonium (Liebig). C 2 H 4 O.NH 3 = C 2 H 3 O.NH 4 It unites with the alkaline acid-sulphites, forming crystal- lizable combinations. It is very apt to become oxidized, being transformed into acetic acid. C 2 H 4 + = C 2 H 4 2 If some aldehyde and a few drops of ammonia be added to a solution of silver nitrate, and a gentle heat be applied, the liquid soon becomes clouded, and the sides of the vessel con- taining it are covered with a brilliant deposit of metallic silver. ALDEHYDE. 501 By the action of sodium amalgam and water, aldehyde fixes two atoms of hydrogen, and is converted into alcohol (A. Wurtz). C 2 H 4 + H 2 = C 2 H 6 When hydrochloric gas is passed into a mixture of aldehyde and absolute alcohol, monochlorether is formed. C 2 H*0 + C 2 H5.0H + HC1 = IPO Monochlorether. Chlorine converts aldehyde into acetyl chloride and other products (A. Wurtz). C 2 H 3 O.H + CP == C 2 H 3 O.C1 + HC1 When treated with phosphorus pentachloride, aldehyde ex- changes its atom of oxygen for two atoms of chlorine, and is transformed into monochlorethyl chloride, C 2 H 4 C1 2 (ethylidene chloride). CH 3 CH 3 PC1! ^ inc.. Aldehyde. Ethj Hdene chloride. Aldehyde has a great tendency to become converted into polymeric modifications. Among these are paraldekyde, which is liquid, and metaldehyde, which is solid (Liebig). Dry hydrochloric acid gas converts aldehyde into ethylidene oxy chloride (an isomeride of dichlorether), eliminating water. 2C 2 H 4 O + 2HC1 = C 4 H 8 C1 2 + H 2 Ethylidene oxychloride. By the action of hydrochloric acid diluted with twice its volume of water, aldehyde doubles its molecule and is converted into a thick, colorless, neutral body, boiling at 95 in a vacuum ; it is soluble in water and reduces ammoniacal silver nitrate. This body is aldol, C 4 H 8 O 2 (A. Wurtz). When heated with ordinary hydrochloric acid, aldehyde gives crotonic aldehyde (Kekule). 2C 2 H 4 O = H 2 + C 4 H 6 Aldehyde. Crotonic aldehyde. The same transformation takes place when aldehyde is heated to 100 with a small quantity of zinc chloride and a trace of water. 502 ELEMENTS OF MODERN CHEMISTRY. ACETYL CHLORIDE. COC1 This body was obtained by Gerhardt in 1852, by treating sodium acetate with pentachloride, or oxychloride of phos- phorus. NaC 2 H 3 2 -f- PCI 5 == C 2 H 3 OC1 + NaCl -f POCP Sodium acetate. Acetyl chloride. Phosphorus oxychloride. It is also formed by the action of chlorine on aldehyde. It is a colorless, mobile liquid, having a pungent odor. It boils at 55. If it be poured into water, it sinks to the bottom, but rapidly decomposes into hydrochloric and acetic acids. C 2 H 3 O.C1 + H 2 = HC1 -f C 2 H 3 O.OH It undergoes a similar decomposition with alcohol, forming ethyl acetate and hydrochloric acid. C 2 H 3 O.C1 -f C 2 H 5 .OH = HC1 -f C 2 H 5 .C 2 H 3 2 With ammonia, it forms acetamide and ammonium chloride. C 2 H 3 O.C1 + 2NH 3 == NH 4 C1 + C 2 H 3 O.NH 2 It reacts with acetates, forming acetic anhydride. TRICHLORACETYL HYDRIDE, OR TRICHLORAL- DEHYDE. (CHLORAL.) This important body was discovered by Liebig and Dumas. It is formed by the prolonged action of chlorine on alcohol. It is a colorless, mobile liquid, having a peculiar, penetrating odor. It boils at 94.4 (Dumas). Gerhardt regarded it as aldehyde in which the three atoms of hydrogen of the radical are replaced by three atoms of chlorine. C 2 H 3 O.H C 2 C1 3 O.H Aldehyde. Chloral. (Acetyl hydride.) (Trichloracetyl hydride.) Its reactions resemble those of aldehyde. It forms crystal- lizable compounds with the disulphites. Its ammoniacal solu- ACETONE. 503 tion reduces silver nitrate. These facts seem to indicate that chloral contains the group CHO, which is characteristic of the aldehydes ; its constitution is then expressed by the formula CCP CHO It regenerates aldehyde by the action of nascent hydrogen (Personne). The alkaline hydrates decompose it into chloroform and a formate (Dumas). C 2 HCPO -f KOH = ECHO 2 + CHOP. Chloral. Potassium formate. Nitric acid converts it into trichloracetic acid, in the same manner that aldehyde is converted into acetic acid. C 2 HCPO -f = C 2 HCP0 2 Chloral forms a crystallizable compound with water, C 2 HCPO CCP + H 2 = l called chloral hydrate. The latter melts at 57, and boils at 98 (Personne), being at the same time decomposed into anhydrous chloral and water. It is very soluble in water. In contact with concentrated sulphuric acid, chloral is rapidly converted into a white, solid substance which is insol- uble in water ; it has the same composition as ordinary chloral, and is called insoluble chloral. Chloral also combines with alcohol, forming alcoholate of chloral (Personne). Chloral hydrate has for some time been successfully employed in medicine as an anodyne and hypnotic. ACETONE. Acetone is the methylide of acetyl, C 2 H 3 O.CH 3 , and since acetyl itself is carbonyl (carbon monoxide) methylide, CH 3 -CO, acetone can be regarded as carbonyl dimethylide, CH 3 -CO-CH 3 . " I 1 CI ro" I CH3 Cl i CH Carbonyl chloride. Carbonyl dimethylide (acetone). Indeed, the synthesis of acetone has been made both by treat- 504 ELEMENTS OF MODERN CHEMISTRY. ing acetyl chloride with zinc methyl (Pebal and Freund), and by treating sodium methyl with chlorocarbonic gas (carbonyl chloride). Zn(CH 3 ) 2 -f 2(C 2 H 3 O.C1) = 2(C 2 H 3 O.CH 3 ) + ZnCl 2 Zinc methyl. Acetyl chloride. Acetone. 2(CH 3 .Na) -f CO j ^} = 2NaCl + CO Sodium methyl. Carbonyl chloride. Acetone. Preparation. Acetone is prepared by distilling dry calcium acetate in a clay retort. The vapors given off are condensed in a well-cooled receiver, and the liquid obtained is distilled on a water-bath with an excess of calcium chloride. Ca(C 2 H 3 2 ) 2 = C 3 H 6 -f CaCO 3 Properties. Acetone is a colorless liquid, having a slightly empyreumatic, ethereal odor. It boils at 56. It dissolves in all proportions in water, alcohol, ether, and wood-spirit. Like aldehyde, it forms crystallizable combinations with the alkaline acid-sulphites. In presence of nascent hydrogen, produced by sodium amal- gam and water, it fixes H 2 and is converted into isopropyl alcohol (Friedel). CH 3 CH 3 CO -f H2 = CH.OH CH3 CH3 Acetone. Isopropyl alcohol. It is seen by this method of formation that isopropyl alcohol contains a group CHOH, united to two methyl groups ; it is a secondary alcohol (page 473). Isopropyl alcohol is not the only product of the action of nascent hydrogen on acetone. The reaction gives rise to a product of condensation resulting from the addition of H 2 to two molecules of acetone. This has received the name pina- cone. 2C 3 H 6 + H 2 = C 6 H W 2 Pinacone. It is a tertiary glycol (see page 522). It constitutes a color- less, crystallizable mass, fusible between 35 and 38, and boil- ing at 171-172. By the action of dilute and hot sulphuric or hydrochloric acid, it loses one molecule of water and is con- ACETAMIDE. 505 verted into a neutral liquid, boiling at 106. This is pinaco- lin, C 6 H 12 0. When acetone is added in small portions to phosphorus pentachloride, a very energetic reaction takes place and two chlorides are formed. One of them, C 3 H 6 C1 2 (methylchlor- acetol), boils at 70. The other, C 3 H 5 C1 (monochloropropy- lene), boils at 23 (Friedel). C 3 H 6 + PCI 5 = C 3 H 6 C1 2 + POC1 3 C 3 H 6 CP = C 3 H 5 C1 + HC1 Hot, concentrated sulphuric acid removes the elements of water from acetone and converts it into a hydrocarbon, which has received the name mesitylene (Kane). 3C 3 H 6 3H 2 = C 9 H 12 Acetone. Mesitylene. ACETAMIDE. C 2 H 3 O.NH 2 This amide may be obtained by heating ethyl acetate to 100 in sealed tubes with aqueous ammonia. Alcohol and acetamide are formed according to the equation C 2 H 5 .C 2 H 3 2 + NH 3 = C 2 H 3 O.NH 2 + C 2 H 5 .OH When the resulting liquid is evaporated in a vacuum, the acetamide remains. It may be purified by distillation, collecting that which passes above 200. Acetamide is also formed by the action of ammonia on acetyl chloride ; one of the readiest methods of preparing it consists in simply distilling ammonium acetate. It is a solid, crystallizable body, soluble in water in all pro- portions. Its odor resembles that of mice. Boiling potassium hydrate reacts with it, forming potassium acetate and ammonia. Phosphoric anhydride removes from it the elements of water, converting it into acetonitrile or methyl cyanide. C 2 H 3 O.NH 2 = C 2 H 3 N + H 2 O ACIDS OF THE SERIES C n H 2n 2 Formic and acetic acids, of which the principal compounds have just been described, are the first terms of a very extensive homologous series. It is the series of volatile fatty acids, so named because it includes a great number of compounds which w 43 506 ELEMENTS OF MODERN CHEMISTRY. were at first obtained from the natural fatty bodies, and which are the fatty acids proper. Among the bodies congeneric with acetic acid, those of which the molecules are less complicated are liquid at ordinary temperatures ; the others are solid. The following table gives the nomenclature, composition, and prin- cipal physical properties of these acids : CRUDE FOKMULJS. CH 2 2 C 2 H*0 2 C 3 H 6 2 OH 8 2 C5H10Q2 C 6 H 12 2 C 7 H U 2 C 8 H 16 2 C 9 H 180 2 RATIONAL FORMULAE. H-CO.OH CH 3 -CO.OH CW-CO.OH C 3 H*-CO.OH C 4 H 9 -CO.OH MELTING- POINTS. 1 17 21 CW-CO.OH 5 14 C 8 H 17 -CO.OH BOILING- POINTS. 99 118 140.7 163 175 199.7 212 236 260 C 12 H 2 *0 2 C 16 H 32 2 C 17 H 3 *0 2 C 18 H 3 6Q 2 C 20 H^0 2 C 22 H 44 2 C 27 H 54 2 CWMXXOH 27.2 c^ii^-co.oH 43.6 C13H27-CXXOH 53.8 C 15 H 31 -CO.OH 62 C 16 H : -CO.OH 60 C 17 H 35 -CO.OH 69.2 C 19 H 39 -CO.OH 75 C^H^-CO.OH 96 C 26 H 53_CO.OH 78 C29 H 59_CO.OH 88 NAMES OF ACIDS. Formic acid .... Acetic acid Propionic acid . . . Butyric acid .... Valeric acid (isovaleric) Caproic acid (isocaproic) CEnanthylic acid . . . Caprylic acid .... Pelargonic acid . . . Capric acid Laurie acid Myristic acid .... Palmitic acid .... Margaric acid .... Stearic acid Arachnic acid .... Benic acid Cerotic acid .... Melissic acid .... We have already noticed the existence of numerous isomeric alcohols, and in their study the principles of isomerism have been explained. Such isomerides exist also in the series of acids, and are caused by the different atomic structure of the radicals, C n H 2n+1 , which figure in the preceding formulse. We will consider two examples. 1. When normal butyl alcohol, CH 3 -CH 2 -CH 2 -CH 2 .OH, is oxidized, normal butyric acid, or the butyric acid of fermentation, is obtained, CH 3 -CH 2 -CH 2 - CO.OH. The acid obtained by oxidation of the butyl alcohol of fermentation is different from this, and the difference is caused by the difference in structure of the radicals (C 3 H 7 )'. Isobutyric acid, derived from the alcohol of fermentation, whose constitution is pTT3^ > CH-CH 2 .OH, contains pr^ CH-CO.OH. The acid is derived from the alcohol by the substitution of for H 2 in the group (CH 2 .OH)'. 2. As we have already seen, the constitution of amyl alcohol of fermentation is expressed by the formula PROPIONIC ACID. 507 3 3 >CH-CH 2 -CH 2 .OH. The valeric acid produced by its oxidation is then But normal valeric acid is also known, and contains CH 3 -CH 2 -CH 2 -CH 2 -CO.OH It results from the oxidation of normal amyl alcohol CH 3 -CH 2 -CH 2 -CH 2 -CH 2 .OH Another interesting isomeride of valeric acid is trimethyl- acetic acid, which was discovered by Boutlerow. If we compare the three isomeric acids, C 5 H 10 2 , with acetic acid itself, we will find that their isomeric relations can be ex- pressed in a very simple manner, by saying that normal valeric acid is propylacetic acid, the acid derived from the alcohol of fermentation is isopropylacetic acid, and lastly, that Boutlerow's acid is trimethylacetic acid. CH3 CH2(C3H7) CH2(CH< C(CH 3 ) 3 CO.OH CO OH CO.OH CO.OH Acetic acid. Propylacetic acid. Isopropylacetic acid. Trimethylacetic acid. We cannot dwell further on the subject; that which pre- cedes is sufficient to elucidate the isomerism of acids of the series C n H 2n 2 . Propionic Acid, C 3 H 6 2 . This acid is formed by the action of potassium hydrate on ethyl cyanide. It is also a product of fermentation ; thus, it has been obtained by allowing a solution of sugar, mixed with chalk and cheese, to ferment during a year. It is also formed in small quantity in the distillation of wood. Wanklyn made its synthesis by passing carbon dioxide over sodium ethyl. CO.O -f C 2 H 5 Na = C 2 H 5 -CO.ONa Sodium propionate. Propionic acid may also be formed, though with difficulty, by the direct combination of carbon monoxide and ethylate of sodium. CO C 2 H 5 .ONa = C 2 H 5 -CO.ONa 508 ELEMENTS OF MODERN CHEMISTRY. Properties. It is a colorless, mobile liquid, having an odor like that of acetic acid. It solidifies at 21, and boils at 140.7. Density at 21, 0.996. It is miscible with water in all proportions. Calcium chloride separates it from its aqueous solution. There are a great number of substitution products directly related to propionic acid. Among these are the chlorine, bro- mine, and iodine derivatives, and the amides. Two of these derivatives are known of each particular species, presenting curious isomeric relations. The following examples will serve as illustrations : CR3 CH3 CH 2 C1 CH3 CH 2 (NH 2 ) CH 2 CHC1 CH 2 CH(NH 2 ) CH 2 C0 2 H C0 2 H C0 2 H C0 2 H CH-CH2-CH2I HI = CH3> CH - C1I=CH2 Amyl iodide. Isopropyletliylene. This body also exists in small quantity in the mixture of hydrocarbons formed by the action of zinc chloride on amyl alcohol. Boiling-point, 25. It unites with hydriodic acid, forming a secondary iodide, (CH 3 ) 2 ^CH-CHI-CH 3 , which boils at 137-139. It combines with bromine, forming the bromide (CH 3 ) 2 =CH-CHBr-CH 2 Br, which boils between 180 and 190. Polymerides of Amylene. By the action of zinc chloride on amyl alcohol, there are formed, independently of amylene, other hydrocarbons, among which are the polymeric modifica- tions known as diamylene, C 10 H 20 ; triamylene, C 13 !! 30 ; tetra- mylene, C 20 H 40 (Balard, Bauer). These bodies are formed by the union of one, two, three, or four molecules of amylene. HYDROCARBONS OF THE SERIES C n H 2 "- 2 . Among the more simple hydrocarbons is one which was dis- covered by E. Davy, and which Berthelot has recently suc- ceeded in preparing by various processes. It is acetylene, and is the first member of a series which includes, among others, the following hydrocarbons : Acetylene C 2 H 2 (E. Davy, Berthelot). Allylene C 3 H 4 (Sawitsch). Crotonylene C 4 H 6 (E. Caventou). Valerylene (W (Reboul). Acetylene, C 2 H 2 = CH^CH. This gas is produced by the incomplete combustion of many organic substances rich in car- bon (Berthelot). If a few drops of ether be poured upon the surface of an ammoniacal solution of cuprous chloride contained in a nar- row jar, and its vapor be ignited, a brownish-red deposit of acetylenide of copper will be formed and may be observed on DIATOMIC ALCOHOLS. 521 flowing the liquid around on the sides of the jar. This reac- tion is characteristic of acetylene. This gas may be formed by the direct union of carbon and hydrogen, as discovered by Berthelot, when the electric arc is passed between carbon points in a vessel containing pure hydro- gen. At the high temperature of the arc, the hydrogen com- bines directly with the carbon, forming acetylene. It is also formed when inonobromethylene is heated with amylate of sodium (the sodium compound of amyl alcohol) (Sawitsch). C 2 H 3 Br + C 5 H n .ONa = C 2 H 2 + C 5 H n .OH + NaBr Mouobrom- Amylate of sodium. Acetylene. Amyl alcohol, ethylene. Acetylene is a colorless gas, having a peculiar and disagree- able odor. It is quite soluble in water. It burns with a bright but smoky flame. It forms two compounds with bromine, a dibromide, C 2 H'W, and a tetrabromide, C 2 H 2 Br 4 . DIATOMIC ALCOHOLS, OR GLYCOLS. The name glycols was given by Wurtz to the dihydrates of the series of hydrocarbons, C n H 2n . If ordinary alcohol be ethyl hydrate, ordinary glycol is ethylene dihydrate. C 2 H 5 .OH C 2 H 4 (OH) 2 Ethyl hydrate. Ethylene dihydrate. While alcohol reacts with a single molecule of a monobasic acid to form a neutral ether, glycol can react with either one or two molecules of a monobasic acid, thus forming two ethers. In other words, while the monatomic alcohols contain but one atom of hydrogen which is replaceable by a single radical of a monobasic acid, glycol contains in the two groups OH two such atoms of hydrogen, capable of being replaced by 2 radicals of a monobasic acid, or one radical of a dibasic acid. (C*H*0 2 )" Ethyl acetate. Ethylene diacetate. Ethylene succinate. The glycols yield diatomic acids by oxidation. There are isomeric glycols, or isoglycoh, corresponding to the isoalcohols which have already been denned (page 473). 44* 522 ELEMENTS OP MODERN CHEMISTRY. Six glycols are now known, belonging to the series C n H 2n+2 2 . DENSITY AT 0. BOILING-POINTS. Ethylene glycol, or glycol . . . C 2 H 6 2 1.125 197.5 Propylene glycol, or propylglycol . C 3 H 8 2 1.051 188-189 Butylene glycol, or butylglycol . C 4 Hi0 2 1.048 183-184 Amylene glycol, or auiylglycol . . C 5 11 12 2 0.987 177 Hexylene glycol, or hexylglycol . C 6 H U 2 0.9667 207 Octylene glycol, or octylglycol (Ph. de Clermont) ....... C 8 H 16 2 It is to be remarked that all of the members of the above series are not, strictly speaking, homologous. The structure of the latter glycols is different from that of ethylene glycol ; they are isoglycols. The propylglycol discovered by Wurtz is of this number. Normal propylglycol has recently been discovered by Geroinont, and obtained in a pure state by Reboul. The isomerism of the glycols, like that of the alcohols, is due to the constitutions of their molecules, which can contain, like the molecules of the alcohols, the following groups : The primary group -CH 2 .OH The secondary group =CH.OH The tertiary group ^C. Thus, ethylene glycol is primary, since it contains two groups, CH 2 .OH. The amylglycol derived from trimethylethylene is at the same time secondary and tertiary. Pinacone, which has already been mentioned (page 504), is a tertiary glycol; it contains two groups ^(C.OH). CH 2 .OH CH3> C>OH J ^ f ' H CH2.0H CH 3 -CH.OH CH> C ' OH Glycol. Amylglycol. Pinacone. (Secondary and tertiary.) (Tertiary.) Among the mixed glycols, that is, those containing at the same time two different alcoholic groups, is ordinary propyl- glycol, which is primary and secondary. CH 2 .OH CH 3 CH2 CH.OH CH 2 .OH CH2.0H Normal propylglycol. Ordinary propylglycol. (Primary). (Primary and secondary). GLYCOL. 523 GLYCOL, OR ETHYLENE DIHYDRATE. C 2 H 6 O 2 = C 2 H*(OH) 2 Wurtz first obtained glycol by causing either iodide or bro- mide of ethylene to react with silver acetate , Ag.C 2 H30 2 rrzmy I C 2 H 3 2 . T CtH*P + A = 1C 2 H30 2 ' Silver acetate. Ethylene diucetate. and saponifying the resulting ethylene diacetate by potassium hydrate. + 2KOH = 2(C 2 H30.0K) + (C*H*)" Ethylene diacetate. Potassium acetate. Glycol. Atkinson has shown that the silver acetate may be advan- tageously replaced by an alcoholic solution of potassium ace- tate. Bromide of ethylene reacts with the latter salt, forming potassium bromide, which is almost insoluble in alcohol, and ethylene acetate which is afterwards decomposed by caustic potassa or caustic baryta. Another process has been recently proposed by Hiifner and Zoller. 188 grammes of ethylene bromide, 138 grammes of potassium carbonate and 1 litre of water are introduced into a large flask connected with a reversed condenser, and the mix- ture is boiled until all of the ethylene bromide has disappeared. The aqueous liquid is then concentrated on a water-bath, and alcohol is added to precipitate the potassium bromide ; the alcoholic liquid is then distilled. Alcohol and water first pass, and when the temperature rises above 150, the liquid which condenses is nearly pure glycol. Properties. Grlycol is a somewhat syrupy, colorless, and odorless liquid, having a sweet taste. It mixes with water and alcohol in all proportions, but is scarcely soluble in ether. It boils at 197.5, and distils without alteration. Its analogy to alcohol, from which it differs by containing one more atom of oxygen, is demonstrated by the following experiments : 1. If platinum black be moistened with glycol and then rapidly plunged into a jar of oxygen, a brilliant incandes- cence is manifested immediately, due to the energetic absorp- tion of oxygen. 524 ELEMENTS OP MODERN CHEMISTRY. With dilute glycol, the oxidation is slower, and glycollic acid is formed. CH2.0II CH 2 .OH CH2.0H + 2 = CO.OH + I12 Glycol. Glycollic acid. 2. If glycol be heated with ordinary nitric acid, torrents of red vapor are disengaged, and the liquid deposits crystals of oxalic acid on cooling. CH2.0H CO.OH CIP.OH + 202 = CO.OH +2I12 Glycol. Oxalic acid. 3. When glycol is heated with potassium hydrate to 250, pure hydrogen is disengaged and potassium oxalate is formed. C 2 H 6 2 -f 2KOH = C'OK 2 -f 4H 2 Glycol. Potassium oxalate. These experiments establish between glycol and glycollic and oxalic acids, relations analogous to those which exist between alcohol and acetic acid. Ethylene Chlorhydrate, or Ethylenic Chlorhydrin. When hydrochloric acid gas is passed into glycol, a neutral compound is formed which constitutes the monochlorhydrm of glycol, or ethylene chlorhydrate. C2H*<^ + HC1 = C 2 H 4 * s obtained as a colorless or slightly yellow liquid, which is sol- uble in water. Density at 11, 1.31. Ethylene dinitrate, C 2 H 4 <', is formed by the action of ethylene bromide on an alcoholic solution of silver nitrate. It is a mobile, colorless liquid, insoluble in water. Density at 8, 1.4837. It explodes by percussion (Henry). Ethylene Acetates. When glycol is heated with acetic acid, it is converted into acetic ethers. C2H3Q.OH = Acetic acid. Ethylene monacetate. C2H4 is obtained. Greene has obtained ethylene oxide by double decomposi- tion, by heating ethylene bromide with anhydrous sodium oxide. C 2 HW + Na 2 = C 2 H 4 + 2NaBr Properties. Ethylene oxide boils at 13.5. It dissolves in all proportions in water, alcohol, and ether. Under the influence of sodium amalgam and water, it fixes hydrogen directly, being transformed into alcohol. C 2 H 4 + H 2 = C 2 H 6 It combines directly with water at 100, regenerating glycol. C 2 H 4 -f H 2 = C 2 H 6 2 It possesses basic properties. If equal volumes of hydrochloric gas and vapor of ethylene oxide be mixed over the mercury-trough (the mercury should be slightly warmed) the two gases will disappear ; they combine to form a liquid which is ethylene chlorhydrate. C 2 H 4 + HC1 = C 2 H 5 C10 If liquid ethylene oxide be added to a cooled solution of magnesium chloride, an abundant precipitate of magnesium hydrate will be formed in the course of a day, and the liquid will contain ethylene chlorhydrate. Oxide of ethylene precipi- tates magnesia as would a powerful base (A. Wurtz). If a fragment of zinc chloride be allowed to fall into ethylene oxide, the latter soon undergoes a curious, polymeric change, and becomes solid (A. Wurtz). Eases Derived from Ethylene Oxide. Oxide of ethylene combines with ammonia, yielding a series of bases, the hydrox- ethylenamines, which are formed by the direct union of one, two, or three molecules of ethylene oxide with one molecule of ammonia. C 2 H 4 .OH ) C 2 H*.OH ") C 2 H*.OH ) H V N C 2 H*.OH [ N C2H*.OH [ N Hj H) C'HiOHj Hydroxethylenamine. Dihydroxethylenamine. Trihydroxethylenaraine. ETHYLENE-DIAMINES. 527 These bases are also formed by the action of ammonia on ethylene chlorhydrate. ) + NH 3 = H V N + HC1 HJ When ethylene chlorhydrate is treated with trimethylamine, the bodies combine, forming a chloride. When this chloride is treated with water and silver oxide, it is converted into a hydrate. C*H*.OH) This hydrate is neurine, an energetic natural base which exists in the bile (choline) and which is also a product of the decomposition of a complex substance, leeithine, which exists in the brain, in the nerves, and in the yolk of eggs. ETHYLENE-DIAMINES. These bases result from the substitution of one, two, or three ethylene groups, (C 2 H 4 )", each for two atoms of hydrogen in two molecules of ammonia. They are formed by the reaction of an alcoholic solution of ammonia on ethylene bromide at ordinary temperatures. C 2 H 4 Br2 + 2NH 3 = C 2 H 4 (NH2)2.2HBr Ethylene-dlamine hydrobromide. CH2-NH' f (CH*)" . Etnylene-diamme, ^ H2 _ NH2 =N * { B ls a hq ul d b^ 6 ? boiling at 123. By the prolonged action of an excess of ethylene bromide, it is converted successively into dieihylene- diamine and triethylene-diamine. (C 2 H*)" f(C 2 H 4 )" f(C 2 H 4 )" Ethylene-diamine. Diethylene-diamine. Triethylene-diamine. Diethylene-diamine boils at 1*70, and triethylene-diamine at 210. They are liquids. The ethlylene-diamines are diacid, that is, they combine with two molecules of a monatomic acid, such as hydrochloric or hydrobromic acid (Hofmann). 528 ELEMENTS OF MODERN CHEMISTRY. ISETHIONIC ACID. This acid, which has long been known, attaches to the ethy- lene derivatives. Oxide of ethylene unites directly with sodium acid-sulphite (bisulphite), forming sodium isethionate. C*H*.0 + N ^>SO' = CH* C2 2 - C2 2 o + POP . POO. + CH2-CCT CHM30CI Succinic anhydride. Sxiccinyl chloride. Kekule has obtained monobromo-succinic and dibromo-suc- cinic acids by heating moistened succinic acid with bromine in sealed tubes. Monobromo-succinic acid is converted into malic acid when treated with water and silver oxide. + AgOH - C*H(OH)< + AgBr Monobromo-succinic acid. Malic acid. Under the same circumstances, dibromo-succinic acid is con- verted into tartaric acid. + 2AgOH = WW(OH)*< + 2AgBr Dibromo-succinic acid. Tartaric acid. These reactions, which were discovered by Kekule. establish very close relations between succinic, malic, and tartaric acids. 552 ELEMENTS OF MODERN CHEMISTRY. C 4 H 6 4 succinic acid. OH 6 5 malic acid. OH 6 6 tartaric acid. The following formulae express the constitutions of these acids : CH 2 -CO.OH CH'-CO.OH CH(OH)-CO.OH iH'-CO.OH CH(OH)-CO.OH CH(OH)-CO.OH Malic acid is oxysuccinic acid, and tartaric acid is dioxysuc- cinic acid. By reducing agents, the latter acids can be con- verted into succinic acid. When either of them is heated with a large excess of hydriodic acid, water is formed, iodine is de- posited, and the liquid will be found to contain succinic acid (Schmitt and Dessaignes). MALIC ACID. OETOs = CO.OH-CH 2 -CH(OH)-CO.OH This acid, which exists in a number of vegetables, was ex- tracted by Scheele from apple-juice. It is generally prepared from the berries of the mountain-ash, gathered before their complete maturity ; they are strongly pressed, and the juice is boiled, filtered, and neutralized with milk of lime at the ordi- nary temperature. Calcium malate is deposited, and this is converted into the acid malate by dissolving it in boiling water acidulated with nitric acid. The calcium acid malate may be readily purified by crystallization, after which it is converted into malate of lead by double decomposition with lead acetate. The lead salt is suspended in pure water and decomposed by hydrogen sulphide ; the solution of malic acid is then filtered and evaporated (Liebig). Properties. Malic acid crystallizes in little needles grouped in rounded grains. These deliquesce when exposed to the air. The aqueous solution of malic acid has a marked acid taste. When long kept, it becomes filled with vegetations. It de- viates the plane of polarization to the left. However, there is an inactive malic acid which has no effect on polarized light ASPARAGIN. 553 (Pasteur). Solution of malic acid does not produce a cloud in lime-water, neither in the cold, nor on boiling. When malic acid is heated, it begins to lose water at 130, and between 150 and 200 is converted into two acids which are isomeric with each other, and are known as maleic and fumaric acids. C 4 H 6 5 C 4 H 4 4 + H 2 Malic acid. Maleic and fumaric acids. By the action of potassium hydrate at about 150, malic acid is decomposed into oxalic and acetic acids. C 4 H 6 O + H 2 O = C 2 H 2 O 4 + C 2 H 4 2 + H 2 Malic acid. Oxalic acid. Acetic acid. ASPARAGIN AND ASPARTIC ACID. Succinic and malic acids present simple and remarkable rela- tions with two nitrogenized bodies which have long been known ; they are asparagin and aspartic acids. The latter body is amidosuccinic acid, and bears the same relations to succinic acid that glycocol (amido-acetic acid) bears to acetic acid. On the other hand, its relations to malic acid are analogous to those of glycocol to glycollic acid. CH 3 Cff'.OH CH2.NH 2 CO.OH CO.OH CO.OH Acetic acid. Glycullic acid. Glycocol. CH2-CO.OH CO(OH)-CO.OH CH(NH2)-CO.OH CH2-CO.OH C II 2 -CO.OH CH 2 -CO.OH Succinic acid. Malic acid. Aspartic or amidosuccinic acid. Asparagin is the monamide of aspartic or amidosuccinic acid ; it is isomeric with the diamide of malic acid. CH(NH 2 )-CO.NII 2 CH.OH-CO.NH 2 CH 2 -CO.OH CH 2 -CO.NH 2 Asparagin. Malamide. Asparagin, C 4 H 8 N 2 3 . This body exists naturally in aspa- ragus, black salsify, the roots of marsh-mallow, licorice wood, and in the buds of cereals, peas, vetches, and beans before they flower. To extract it from these vegetables, they are expressed while fresh, and the juice is clarified and concentrated. The asparagin is deposited in colorless crystals. It is only slightly soluble in cold water and alcohol, but is more soluble in hot water. It forms combinations with both bases and acids. Y 47 554 ELEMENTS OF MODERN CHEMISTRY. When boiled with these agents, it loses ammonia and is con- verted into aspartic acid. C 4 H 8 N 2 3 -f H 2 = NH 3 = C 4 H 7 N0 4 Asparagin. Aspartic acid. Aspartic Acid, C 4 H 7 N0 4 , forms rhombic crystals, slightly soluble in cold, and more soluble in hot water. Like glycocol, aspartic acid can form compounds with both acids and bases. TARTARIC ACID. C*H 6 6 = CO.OH-CH(OH)-CH(OH)-CO.OH This important acid was discovered by Scheele in the tartar, or argol, which is deposited in casks in which wine is kept. It is pTepared from purified tartar, called cream of tartar, which is acid tartrate of potassium. Preparation. The salt is dissolved in boiling water, and chalk is added until all effervescence, due to the disengage- ment of carbon dioxide, ceases. Insoluble calcium tartrate is deposited, and potassium neutral tartrate remains in solution. The calcium tartrate is collected on a filter, and the filtrate is precipitated by calcium chloride. A new portion of insoluble calcium tartrate is thus obtained, and is washed and united with the first portion. This salt is then suspended in water and exactly decomposed by dilute sulphuric acid ; calcium sulphate is precipitated, and separated by filtration, and the filtered liquid, when sufficiently concentrated and allowed to evaporate in a warm place, deposits crystals of tartaric acid. Properties. Tartaric acid crystallizes in large, oblique rhom- bic prisms, which often present hemihedral facettes. They are unaltered by the air, and dissolve in about half their weight of cold water and still more abundantly in boiling water. They dissolve also in alcohol, but not in ether. The aqueous solution of tartaric acid turns the plane of polarization to the right. It forms white precipitates in lime- water and baryta-water, but an excess of the acid redissolves these precipitates. If an excess of tartaric acid be added to a solution of cupric sulphate, the liquid may be saturated with potassium hydrate, but no precipitation of cupric hydrate will take place. The liquid will remain transparent and will assume a beautiful dark-blue color ; it is called cupro-potassic solution. In the TARTARIC ACID. 555 same manner, ferric chloride, to which tartaric acid has been added, is not precipitated by an excess of potassium hydrate. When tartaric acid is fused with potassium hydrate, it is decomposed into acetic and oxalic acids. 2 C 2 H 2 4 Action of Heat on Tartaric Acid. 1. Tartaric acid fuses between 170 and 180, and when the action ot the heat is not prolonged, it is converted into an isomeric acid, called meta- tartaric. 2. If the acid be maintained for some time in fusion, it loses water and is converted into ditartaric acid. 2C*H 6 6 = C 8 H 10 U -f- H 2 Ditartaric acid. 3. When 15 or 20 grammes of tartaric acid are suddenly heated over a naked fire for four or five minutes, the mass swells up and a deliquescent, yellow, spongy mass is obtained, which constitutes what is called tartaric anhydride. C 4 H 6Q6 = C4H 4 5 + H 2 O Tartaric anhydride. When heated for some time to 150 in a hot-air oven, tar- taric anhydride becomes insoluble. 4. When tartaric acid is distilled by heating it gradually in a retort to 300, it is transformed into two pyrogenous acids, pyruvic and pyrotartaric acids. OH 6 6 = C 3 H 4 3 + CO 2 + H 2 Pymvic acid. 2C 4 H 6 6 =3 C 5 H 8 O + 3C0 2 + 2H 2 O Pyrotartaric acid. It is seen that these acids, produced by the action of heat on a complex organic acid, differ from the latter only by the elements of water and carbon dioxide. Such is the law of pyrogenous acids established by Pelouze. When tartaric acid is heated to 1*70, in sealed tubes, with water, it undergoes a remarkable modification : it is converted into paratartaric acid and inactive tartaric acid ; the latter is so named because it is without action on polarized light, and cannot be broken up, as can paratartaric acid, into a dextrogy- rate and a levogyrate acid (Jungfleisch). Action of Nitric Acid upon Tartaric Acid. Very con- centrated nitric acid converts tartaric acid into nitrotartarit 556 ELEMENTS OF MODERN CHEMISTRY. add, C 4 H 4 (N0 2 ) 2 6 (Dessaignes). This body may be obtained in crystals, but it is not stable. Its aqueous solution decom- poses between 40 and 50, with a brisk effervescence of carbon dioxide, and formation of oxalic acid. When the decompo- sition takes place below 36, a peculiar, crystallizable acid is formed, which Dessaignes has named tartronic acid. Its com- position corresponds to the formula C 3 H 4 5 == C 3 H 2 3 (OH) 2 . TARTRATES. Tartaric acid is dibasic ; it contains two hydrogen atoms which are replaceable by an equivalent quantity of metal. Neutral tartrates and acid tartrates are known. II 1 OH*0 " I C*H*0 6 ?J' 1 CPH*0, or R"C*H*0* 11 J ivi ) ivi j Tartaric acid. Acid tartrates. Neutral tartrates. Neutral tartrates are known in which one atom of metal is replaced by a monatomic oxidized group, such as (SbO)', (FeO/, (BoO)'. H } C4H4 6 (SbOr } C4II4 6 (FeOr } C4H4 6 (BoO^' } G * Potassium Tartar-emetic. Ferro- potassium tartrate. Boro-potassium acid tartrate. tartrate. Potassium Acid Tartrate, or Cream of Tartar, KHC 4 H 4 6 , is prepared from the crude tartar of wine-casks by subjecting that product to several crystallizations in boiling water. It crystallizes in right rhombic prisms, very slightly soluble in water. If a concentrated solution of tartaric acid be added to a saturated solution of potassium chloride, a precipitate of potassium acid-tartrate will be formed on agitating the liquid. Potassium Neutral Tartrate, K 2 C 4 H 4 6 . This salt is pre- pared by neutralizing a boiling solution of cream of tartar with potassium carbonate. The evaporated solution deposits on cooling oblique rhombic prisms, very soluble in water. Potassium and Sodium Tartrate, N f t } C*H*O -h 4H20.-This salt, which is much used in medicine, was discovered in 1672 by Seignette, a pharmacist of Rochelle ; hence it is often called Rochelle salt-, or Seignette's salt. It is prepared by neutralizing a boiling solution of cream of tartar with sodium carbonate, and evaporating the solution. On cooling, the double tartrate is deposited in large, beautiful crystals, eight-sided right rhombic prisms. ANTIMONIO-POTASSIUM TARTRATE. 557 ANTIMONIO-POTASSIUM TARTRATE, OR TARTAR- EMETIC. This salt is prepared by boiling cream of tartar with water and oxide of antimony, which dissolves abundantly in tho liquid. After nitration and cooling, the salt is deposited in crystals which are purified by a second crystallization. Tartar-emetic crystallizes in rhombic octahedra, and the crys- tals, which contain one molecule of water of crystallization for two molecules of salt, effloresce in dry air. Its taste is astringent and nauseating. It dissolves in 14.5 parts of cold water and in about two parts of boiling water. It is insoluble in alcohol. When heated to 200 it loses the elements of water and is converted into a double tartrate of antimony and potassium, in which the trivalent antimony replaces 3 atoms of hydrogen in the tartaric acid. C 4 tP(SbO)'K0 6 = OHW'HKO 6 + H 2 O When heated to redness in a small, covered crucible, tartar- emetic leaves an alloy of potassium and antimony, disseminated in a mass of charcoal. When this mass is exposed to moist air, it suddenly takes fire and explodes, projecting brilliant sparks. The following are the characteristics of a solution of tartar- emetic : Hydrogen sulphide forms an orange precipitate of antimony sulphide. A few drops of hydrochloric acid cause the appearance of a white precipitate of antimony oxychloride, which disappears in an excess of acid. Potassium hydrate produces a white precipitate of antimony oxide, which redissolves in an excess of alkali. A plate of tin immersed in a solution of emetic precipitates metallic antimony as a black deposit. Tartar-emetic is a much employed medicine. In large doses, or smaller ones frequently repeated, it is an energetic poison. Ferro-Potassium Tartrate. This salt is prepared by dis- solving ferric hydrate in cream of tartar, and evaporating the 47* 558 ELEMENTS OF MODERN CHEMISTRY. solution. It forms brown, amorphous scales, very soluble in water. It is used in medicine. Boro-potassium Tartrate is formed when boric acid is dis- solved in a boiling solution of cream of tartar. It is an amor- phous salt, very soluble in water. PARATARTARIC ACID. C 8 H 12 12 + 2H 2 O This acid, which is isomeric with tartaric acid, exists in cer- tain tartars. It was discovered in 1822 by Kestner, and has been studied by Berzelius and by Pasteur. It crystallizes in transparent, dissymetric prisms, which efflo- resce in the air, losing their water of crystallization. It dis- solves in 5.7 parts of water at 15. Its solution does not change the plane of polarized light, but Pasteur has succeeded in separating it into two other acids, both of which are optically active. One of them turns the plane of polarization to the right, and is ordinary tartaric acid; the other deflects it to the left, and is levo-tartaric acid. These two acids, which are iso- meric with each other, reproduce paratartaric acid when they are mixed in equivalent proportions. It is somewhat remark- able that the mixture of their solutions is attended by a development of heat (Pasteur). The solution of paratartaric acid precipitates solutions of sulphate, nitrate, and chloride of calcium, a character which tartaric acid does not possess. Independently of dextro-tartaric acid, levo-tartaric acid, and paratartaric acid, there is a fourth isomeride, which is inactive tartaric acid. It exerts no action on polarized light, and cannot be separated into two active acids (Pasteur). Jungfleisch has shown that these various modifications of tar- taric acid may be produced at will by the action of a tempera- ture of about 1*70 on a solution of ordinary tartaric acid. CITRIC ACID. This acid, discovered by Scheele in 1784, is largely diffused throughout the vegetable kingdom. It exists in lemons, oranges, limes, currants, raspberries, cherries, etc. It may be advantageously prepared from lemon-juice, which URIC ACID. 559 is allowed to stand until it begins to ferment, and is then filtered, and saturated with chalk while boiling. The precipitate of calcium citrate is washed with boiling water, and decomposed by a slight excess of dilute sulphuric acid. The liquid sepa- rated from the calcium sulphate yields crystals of citric acid after concentration. This acid forms large, colorless crystals, derived from a right rhombic prism. It dissolves in three-fourths its weight of cold and half its weight of boiling water. When heated, it melts. At 175 it disengages water, and is transformed into a pyrogenous acid, which is identical with the acomtic acid that may be extracted from aconite. C 6 H 8 7 = C 6 H 6 6 H 2 Aconitic acid. If the heat be increased, carbon dioxide is disengaged, inde- pendently of some accessory products, and oily streaks appear in the neck of the retort, and solidify to a crystalline mass. This product is itaconic acid. A portion of the distilled product remains liquid ; it is the anhydride of a third pyroge- nous acid, isomeric with the preceding, and called citraconic acid. C 6 H 6 6 = C 5 H 6 O + CO 2 Aconitic acid. Itaconic and Citraconic acids. C 5 H 6 4 = C 5 H 4 3 4- H 2 Citraconic acid. Citraconic anhydride. Fused potassium hydrate converts citric acid into oxalic and acetic acids. C 6 H 8 7 -f H 2 O = C 2 H 2 4 -f 2C 2 H 4 2 The solution of citric acid has an acid reaction and a very sour taste. It does not precipitate lime-water in the cold, but the solution becomes clouded after boiling. Citric acid is tribasic. Magnesium citrate, which is soluble, is employed in medi- cine ; it is a purgative, having a sweetish taste. Ferric citrate also is used in medicine. URIC ACID. This body is related to the complex organic acids which have just been studied. Among the numerous products de- 560 ELEMENTS OF MODERN CHEMISTRY. OTT rived from its oxidation, we may mention oxalic acid, C 2 2 <' rktT , OH and an acid, C 3 3 O 5 C 6 H 8 (N0 2 ) 2 5 C 6 H 7 (N0 2 ) 3 5 Cellulose. Dinitrocellulose. Tri nitrocellulose. Gun-cotton looks like cotton, but is more harsh to the touch and sometimes has a light yellowish tint. It burns with a sudden flash, leaving no residue, and produces a great volume of gaseous products consisting of carbon monoxide, carbon dioxide, nitrogen dioxide, etc., and vapor of water. Gun-cotton is insoluble in water, alcohol, ether, chloroform, and the cupro- ammoniacal solution. It is more or less soluble in a mixture of alcohol and ether, and the solution is employed in surgery and photography under the name collodion. Pure trinitrocellulose is, however, insoluble in alcoholic ether. When pyroxylin is heated with a concentrated solution of ferrous chloride, nitrogen dioxide is disengaged, and cellulose is regenerated (Bechamp). GLUCOSIDES. The glucosides are complex compounds, which break up under various conditions, fixing the elements of water and GLUCOSIDES. 587 yielding glucose and other bodies, just as the compound ethers, in fixing the elements of water, are decomposed into alcohols and acids. This definition seems to relate the glucosides to the com- pound ethers, a relation with seems legitimate, since it has been shown by the experiments of Berthelot that glucose has the function of a polyatomic alcohol. Various immediate principles of vegetable origin can be classed as glucosides. We may mention particularly the fol- lowing : GLUCOSID-S. FORMULAS. ORIGIN. Amygdalin .... C 20 H 27 N0 11 bitter almonds. Salicin ..... C 13 H 18 7 willow and poplar bark. Populin ..... C 2 U 22 8 bark and leaves of the aspen. Phloridzin .... C 21 H 24 10 bark and roots of fruit-trees. Arbutin ..... C 12 H 16 7 leaves of the Arctoataphylos uva nrsi. Convolvulin . . . . 0H CH5-C0 2 H C 6 H*< C6H3(C0 2 H) 3 C(C0 2 H)6 Benzol. Ben/oic acid. Phthalic acid Trimesic acid Mellic acid. and isomerides. and isomerides. 7. In the homologues of benzol, the substitution of Cl, Br, OH, NH 2 , C0 2 H, etc., for hydrogen, may take place either in the benzol nucleus or in the lateral chain : isomeric compounds are thus formed. a. By substitution of one atom of chlorine for an atom of hydrogen in toluol, two isomeric compounds, C 7 H 7 C1, may be obtained. In one, the chlorine will be attached to the lateral chain ; in the other, it will be attached to the benzol nucleus, as is the group CH 3 itself. CH-CH OT'-CIPCI CH*<^ H3 Toluol. Benzyl chloride. Chlorotoliiol. b. The phenols result from the substitution of OH for an atom of hydrogen in the nucleus. If this substitution take place in a lateral chain, an aromatic alcohol, isomeric with the corresponding phenol, is obtained. 50* 594 ELEMENTS OF MODERN CHEMISTRY. Toluul. Benzylic alcohol. Crcsol. c. The substitution of a carboxyl group, C0 2 H, for an atom of hydrogen in the benzol nucleus of toluol, C 6 H 5 -CH 3 , pro- duces the aromatic acids, toluic acid, and its isomerides ; if, however, the carboxyl replace a hydrogen atom in the lateral chain, CH 3 , alpha-toluic acid, isonieric with the preceding acids, results. Toluol. Toluic acids. a-toluic acid. d. When two groups OH are substituted for two atoms of hydrogen in the principal chain, oxyphenols are formed. /CH 3 CH 3 -OH ^OU Orcin. e. The substitution of the group NH 2 for one atom of hydro- gen in the principal chain, on the one hand, and in the lateral chain, on the other, produces isomeric alkaloids. C6H5-CH(NH2) Benzylamine. Toluidine. 8. This is not all ; the lateral chains may be grafted at dif- ferent points of the benzol nucleus by substitution for the dif- ferent hydrogen atoms. Their positions and their relative dis- tances from each other are the causes of numerous isomerisms. It is important to understand the principle of this isomer- ism. Let us consider the most simple case, that in which two atoms of hydrogen are replaced by two other mon atomic atoms or monatomic groups. Such compounds are the di- substituted derivatives of benzol, and experiment has shown that there are three di-substituted derivatives of each kind. Thus there are three hydrocarbons containing two groups CH 3 , each substituted for one atom of hydrogen in benzol ; three phenols, each containing two groups OH ; three acids, each containing one group CO 2 H, and one group OH, substi- tuted each for one atom of hydrogen, and three acids, each containing two carboxyl groups substituted for two atoms of hydrogen. Indeed, this substitution may take place in three different ways. The six carbon atoms forming a closed chain and a hydrogen atom being attached to each carbon, the re- AROMATIC COMPOUNDS. 595 placement of two atoms of hydrogen may affect two adjoin- ing atoms of carbon, or two atoms of carbon separated by a third atom of carbon which still retains its H, or lastly, two carbon atoms which are separated by two other carbon atoms, each of which still retains its H. The relative positions of the groups being different in each case, it results that the molecules present different structures and are consequently isomeric. The following examples will explain this kind of isomerism. OrtAo-derivatives are those in which the hydrogen of two adjacent carbon atoms is replaced; raeta-derivatives are those in which the two carbon atoms affected are separated by a third ; para-derivatives are those in which the two carbon atoms are separated by two others. 02 CH 3 OH OH C0 2 H W > A A A A |j HC C-CH 3 HC C-OH HC C-C0 2 H HC c-com s HC^ OH HC x J3H HC K CH HC CH B ^ / ^ / Q V c C C 6 H H H H H Orthoxylol. Orthodiphenol Orthoxybenzoic Orthophthalic P5 (pyrocatechin). acid acid O (salicylic). (phthalic). CH 3 OH OH C0 2 H i ^C A C c // \ /, \ H HC' N CH KG S CH HC CH HC CH HC x C-CH 3 HC s C-OH HC C-C0 2 H HC C-C0 2 H V / ^ / ^ xx c x *c' C C ^ H H H H 1 Metaxylol. Metadiphenol (resorcin). Metoxybenzoic acid Metaphthalic acid (isophthalic). (oxybenzoic). S CH 3 OH OH C0 2 H A A C //Cx H // \ IIC X CH HC' CH HC CH HC X S CH 3 H6 CH HC CH HC xN CH HC s CH. A, / ^ / C C ^G *C 3 CH 3 OH C0 2 H C0 2 H P] Paraxylol. Paradiphenol Paroxybenzoic Pai-aphthalic acid (hydroquinone). acid. (teraphthalic). 596 ELEMENTS OP MODERN CHEMISTRY*. These indications will suffice to illustrate the class of isomer- ides under consideration. With the tri -substituted derivatives of benzol, theory foresees and experiment has demonstrated the existence of still more numerous isomerides, but we cannot dwell on them here. Two very important hydrocarbons are now considered as directly related to benzol. They are naphthalene, C 10 H 8 , and anthracene, C U H 10 . Naphthalene is formed by the union of two benzol nuclei, two atoms of carbon being common to each nucleus (Erlen- ineyer). Anthracene results from the union of two benzol nuclei by the intermediation of two carbon atoms, which are themselves combined together, each by one atomicity, and each of which is combined with one atom of hydrogen (Graebe). These ideas are indicated in the following graphic formulae, which express the reciprocal relations between the atoms of carbon and hydrogen, but not their real positions in space. The latter might be better indicated by a polyhedral form. H H H H H ,C C C C H C '/ ^ // \ / *\ // \ i / >N HC CH HC C CH HC C-C-C CH HC CH HC C CH HC C-C-C CH v v v y H v H H Benzol. Naphthalene. Anthracene. We must with these brief indications conclude the considera- tion of the principles of Kekule's theory, which includes very many compounds. These are the aromatic compounds in the strict, sense of the word. Before undertaking their study, we will briefly describe oil of turpentine and some of the bodies allied to it. OIL OF TURPENTINE AND ITS ISOMERIDES. A large number of hydrocarbons are known having the com- position C 10 H 16 . Some are the natural products which consti- tute the whole or part of the numerous essential oils. Others are the products of art. Among the first are the oils of turpentine, lemon, orange, bergamot, orange-flower, juniper, savin, lavender, cubebs, co- paiba, eleini, pepper, cloves, etc. TURPENTINE. 59V These oils are liquids ; some of them are mixed with oxy- genized solid bodies which are deposited in time, and which were formerly designated as stearoptenes. They are obtained by distilling the vegetable products which contain them with water, for, although the boiling-points of these oils are between 150 and 200, they distil readily with aqueous vapor, and collect in the form of a layer on the sur- face of the condensed water. The more ordinary process consists in passing a current of steam through the plants or aromatic vegetables. For this purpose they are placed on a diaphragm, M (Fig. 129), which T' M FIG. 120. is fixed above the bottom of an ordinary still. The head of the still is then adjusted, connection is made with a condenser, and a current of steam is passed in by the tube TT'T", which penetrates into the still. The steam carries with it the essen- tial oil, which diffuses in it by virtue of the high tension of the vapor of these oils at 100. The mixed vapors rise into the head of the still and condense in the condensing worm. The condensed water, generally clouded by little drops of the essential oil, is received in a vessel of peculiar form, which is called a Florentine receiver. It is shaped like an ordinary flask (Fig. 130), having at its bottom a tube which curves upwards, in the form of a swan's neck, and the upper part of which is but little below the mouth of the flask. As the condensed water and oil collect in this ingenious apparatus, the oil separates and floats on the water ; as the distillation continues, the liquid rises not only in FIG. 130. 598 ELEMENTS OP MODERN CHEMISTRY. the flask, but in the lateral tube, until the water, which is always in large excess, reaches the level of the curved neck and flows off alone, the lighter oil accumulating in the flask. Among the essential oils whose composition is represented by the formula C 10 H 16 , the most important is oil of turpentine, which is obtained by distilling the turpentine of commerce with water. Turpentine is a mixture of resin and essential oil, and flows from incisions cut in the trunks of trees of the genera Pinus, Abies, Picea, Larix. When this resinous substance is distilled with water, the oil passes over and the resin remains ; the latter is called colo- phany, or rosin. Turpentine. Bordeaux turpentine, which comes from the Pinus maritima (Pinus Pinaster), yields, by distillation with water, an essential oil which boils at 156, and turns the plane of polarization to the left. Density at 0, 0.877. Australine, or English oil of turpentine, which comes from the Pinus Australis, has the same boiling-point as the preced- ing, but turns the plane of polarization to the right. Density at 16, 0.864 (Berthelot). American oil of turpentine, derived from Pinus palustris, is also dextrogyrate. Metamorphoses of Oil of Turpentine. 1. When exposed to the air, oil of turpentine gradually absorbs oxygen, becomes yellow and partly resinified. This slow oxidation is due to the production of ozone, with which the oil becomes charged ; it then possesses oxidizing properties (page 61). 2. Concentrated nitric acid oxidizes oil of turpentine with such energy that the mixture sometimes takes fire. When boiled with dilute nitric acid, it forms teraphthalic acid, rT) 2 IT C 6 H 4 <^Q 2 rrj one of the isomerides of phthalic acid (Cailliot). 3. When a mixture of alcohol, nitric acid, and oil of turpentine is left to itself for some time, the latter substance fixes the ele- ments of three molecules of water and is converted into a crys- tallized solid body, C 10 H 20 2 -f H 2 0, called terpin. 4. When oil of turpentine is mixed with -^ its weight of concentrated sulphuric acid, and the mixture is agitated, it is converted into an isomeric hydrocarbon, terebene, which boils at 156, and a polymeric hydrocarbon, C 20 H 32 , which boils between 310 and 313 (H. Dcville). By reason of the re- ducing action which the oil of turpentine exerts on the sul- phuric acid, and which produces sulphurous oxide and water, TURPENTINE. 599 two atoms of hydrogen are removed from the molecule C 10 H 16 , and, independently of terebene, a certain quantity of cymene, C 10 H U , is formed (Riban). C 10 H 16 -f S0 4 H 2 = C 10 H U + SO 2 -f 2H 2 5. The hydracids combine with oil of turpentine. Three com- pounds of turpentine and hydrochloric acid are known. A solid hydrochloride, C 10 H 16 .HC1, is deposited from cooled oil of tur- pentine by the action of gaseous hydrochloric acid, and is called artificial camphor. It is levogyrate, or dextrogyrate, accord- ingly as it has been prepared from turpentine or australine. The crystals are deposited from a very acid, colorless liquid, con- taining a liquid combination of turpentine and hydrochloric acid. When oil of turpentine is left for a month in contact with very concentrated hydrochloric acid, a dihydrochloride is formed, C 10 H 16 .2HC1. It is a solid body, and is identical or isomeric with the artificial camphor of oil of lemon, obtained by passing hydrochloric acid gas into oil of lemon. 6. Antimony trichloride transforms oil of turpentine into a solid polymeride, tetraturpentine. Terebene. Terebene, which has already been mentioned, boils at 156, like its isomeride, oil of turpentine, from which it differs by being optically inactive ; it forms no crystalline hydrate corresponding to terpin, and it never yields a dihy- drochloride. Like turpentine, it forms a crystalline monohy- drochloride when subjected to the action of hydrochloric acid gas (Riban). Camphenes. When dextro- or levo-artificial camphor is heated to between 200 and 220 with sodium stearate, HC1 is removed, and the camphor is transformed into a solid, crys- tallizable hydrocarbon, fusible at 146, and boiling at 160. It is camphene, and is optically active in the same direction as the hydrochloride, from which it is derived. The sodium stearate here acts as a feeble alkali ; when it is replaced by sodium benzoate, inactive camphene is set at lib- erty. The camphenes yield only monohydrochlorides by the action of hydrochloric acid gas (Berthelot). The hydrochlorides of turpentine, terebene, and camphene are isomeric ; the first is almost undecomposable by water at 100, the second loses all of its hydrochloric acid by the action of boiling water, and it is the same with the third, which, how- ever, regenerates solid camphene (Riban). 600 ELEMENTS OF MODERN CHEMISTRY. Isoturpentine. When oil of turpentine is heated to 300, it is transformed into a new isomeride, which is active and levogyrate: it is isoturpentine, and boils towards 176. Den- sity at 0, 0.859. At the same time as isoturpentine, meta- turpentine is formed, C^H 32 , boiling at 360. Terpilene. This is another isomeride of oil of turpentine, and boils at the same temperature. It is obtained by removing all of the hydrochloric acid from the dihydrochloride, C 10 H 16 2HC1, by the action of either sodium (Berthelot) or aniline (Lauth and Oppenheim). It is characterized by the fact that it yields a dihydrochlo- ride with great ease by the action of gaseous hydrochloric acid, and does not form a monohydrochloride. Citrene, C 10 H 16 . This hydrocarbon is contained in oil of lemon, together with an oxygenized body. It is a colorless liquid, having an agreeable odor. It boils at 173-174. Den- sity at 15, 0.85. Citrene unites readily with hydrochloric acid, producing a crystalline dihydrochloride of citrene. C 10 H 16 .2HC1, fusible at 14. ORDINARY CAMPHOR, OR LAUREL CAMPHOR. Camphor exists in all of the organs of the Laurus camphora, a tree of China, Japan, and the islands of the Bay of Sundy. When the wood is chipped and distilled with water, the cam- phor volatilizes and condenses in rice-straw, with which the heads of the stills in which the operation is conducted are filled. The product thus obtained in the form of small crystals is re- fined by sublimation in glass vessels heated on a sand-bath. A camphor identical with laurel camphor is deposited from the oil of Matricaria parthenium when the latter is cooled. It is matricaria camphor. Camphor forms a semi-transparent, crystalline mass. Its odor is strong and aromatic ; its taste, bitter and burning. It melts at 175, and boils and distils without alteration at 204. Its density at is 1.0. At ordinary temperatures, the ten- sion of its vapor is so great that it sublimes spontaneously in the vessels in which it is kept. Camphor is almost insoluble in water; when thrown in CAMPHOR. 601 small fragments on the surface of that liquid, it executes gyra- tory movements. It dissolves in alcohol and ether, and the al- coholic solution rotates the plane of polarization to the right. Camphor is inflammable, and burns with a smoky flame. The following are its principal reactions : 1. When heated with phosphoric anhydride, or with chloride of zinc, it loses the elements of water and is converted into a hydrocarbon called cymene. C 10 H 16 = H 2Q _|_ C 10 H H Camphor. Cymene. 2. Camphor appears to be an aldehyde. Although it does not fix hydrogen directly, it can nevertheless be converted into a compound, C 10 H 18 0, which is borneol, or Borneo camphor. This is accomplished by the action of sodium, which replaces the hydrogen of a portion of the camphor, forming a sodium- camphor, while the displaced hydrogen is fixed upon another portion of camphor (Baubigny). According to this reaction, corroborated by the inverse re- action, which will be indicated farther on, the same relations seem to exist between borneol and camphor as between alco- hol and aldehyde. C 2 H 4 C 2 H 6 O Aldel.y.Ie. Alcohol. C 10 H 16Q C 10 H 18 Camphor. Borneol. 3. When camphor is heated for a long time with an alcoholic solution of potassium hydrate, it is decomposed into an acid and an alcohol, which is borneol (Berthelot). 2C 10 H 16 + KOH = C 10 H 15 K0 2 -f C 10 H 18 Camphor. Potassium camphate. Borneol. 4. When vapor of camphor is passed over soda-lime, heated to about 300, the sodium salt of campholic acid is obtained (Delalande). C io H i6 O + NaOH _ c io H 17 Na0 2 Camphor. Sodium campholate. 5. When camphor is subjected to the action of aqueous hypochlorous acid, it is converted into monochloro-camphor, C 10 H 15 C10, which constitutes a colorless, crystalline mass, slightly soluble in water, freely soluble in alcohol and ether, and fusible at 95. 2A 51 602 ELEMENTS OF MODERN CHEMISTRY. 6. By the action of bromine on camphor at 100 or 120, monobromo - camphor, C 10 H 15 BrO, and dibromo - camphor, C 10 H 14 Br 2 O, are formed. These bodies crystallize in colorless prisms. The first fuses at 76, the second, at 114. A bromide of camphor, C 10 H 16 OBr 2 , is also known; it is formed by the action of bromine on a solution of camphor in chloroform. It is a crystalline body which decomposes spon- taneously, especially by the action of light, losing hydrobromic acid and being converted into monobromo-camphor. 7. Camphor absorbs hydrochloric acid gas, forming an oil which is instantly decomposed by water, regenerating camphor. Cold nitric acid dissolves it, forming an oily liquid which is de- composed by water, camphor being precipitated. 8. When camphor is boiled with nitric acid, it is oxidized and converted into camphoric acid. C io H i6 _j_ 3 = c io H 16 4 Camphor. Camphoric acid. BORNEOL, OR BORNEO CAMPHOR. C 10 H 18 O This camphor is extracted from the Dryobalanops aromatica, a tree which grows in the Sundy Islands. Berthelot has ob- tained it by the action of an alcoholic solution of potassa on ordinary camphor. It occurs in small, colorless, transparent, and friable crystals. Its odor recalls at the same time that of camphor and that of pepper. Its taste is burning. It melts at 198, and boils at 212. It turns the plane of polarization to the right. It is insoluble in water, but dissolves readily in alcohol and in ether. When treated with cold, fuming nitric acid, it loses H 2 , and is converted into ordinary camphor, C 10 H 16 0. BENZOL. C 6 H This important body was discovered in 1825 by Faraday. Mitscherlich obtained it by heating benzoic acid with an excess of lime. C 7 H 6 2 == CO 2 + C 6 H 6 Benzoic acid. Benzol. It is now obtained in large quantities from coal-tar by dis- tilling the latter body. The more volatile products contain the BENZOL. 603 benzol, which is purified by fractional distillation. That which passes below 85 is principally benzol, and the latter crystal- lizes out when the liquid which passes between 80 and 85 is cooled to 5. The crystals are collected and separated by expression from the product remaining liquid. They constitute pure benzol.* Berthelot has recently made the direct synthesis of benzol by exposing acetylene to a temperature near redness. 3C 2 H 2 = C 6 H 6 Acetylene. Benzol. Benzol is a colorless, strongly refracting liquid. At 0, it solidifies to crystals which melt at 5.5. It boils at 80.5. It is insoluble in water, but dissolves in alcohol and ether. It is inflammable, and burns with a bright, smoky flame. When long agitated with fuming, or even ordinary sulphuric acid, it dissolves, forming phenylsulphurous acid. C 6 H 6 + JpgQ* = JJ2Q + - C 6 H 5g 3 H Phenylsulphurons acid. When heated to 275 or 280 for twenty-four hours with 80 to 100 parts of concentrated hydriodic acid, benzol is converted into hexane, C 6 H U , iodine being set free. Action of Chlorine and Bromine on Benzol. In sun- light, benzol can absorb directly six atoms of chlorine, forming benzol hexachloride, C 6 H 6 C1 6 , crystallizable in brilliant plates. Another product of the action of chlorine on benzol is mono- chlorobenzol, C 6 H 5 C1, a liquid, boiling between 135 and 137. An excess of bromine in sunlight converts benzol into a solid bromide, C 6 H 6 Br 6 . Monobromobenzol, C 6 H 5 Br, may be made by mixing benzol and bromine in the proportion of one molecule of the first to two atoms of the second, and leaving the mixture to itself for a week at the ordinary temperature. It is then washed, first with water then with potassa, and distilled. Monobromobenzol boils at 152-154. When heated with sodium, it yields to the C 6 H 5 latter its bromine, and a hydrocarbon C 12 H 10 = i ., called C M D diphenyl, is obtained. Dibromobenzol, C 6 H 4 Br 2 , is readily formed by the action of an excess of bromine on benzol. It crystallizes in beautiful prisms, fusible at 89. It boils at 219. # Benzol must not be confounded with the benzine derived from petro- leum, which is a saturated hydrocarbon. 604 ELEMENTS OF MODERN CHEMISTRY. Nitrobenzol, C 6 H 3 (N0 2 ). If benzol be poured in small portions into monohydrated nitric acid, and water be added to the mixture, an oily, yellow liquid separates, constituting nitro- benzol. C 6 H 6 + HNO 3 = H 2 + C 6 H 5 (N0 2 ) It is benzol in which one hydrogen atom is replaced by the group (NO 2 )'. Nitrobenzol is a yellowish liquid, having a strong odor of bitter almonds. It boils at 205, and solidifies at 3. It is employed in perfumery under the name essence of Mirbane. By the action of reducing agents, such as hydrogen sulphide, ammonium sulphide, tin and hydrochloric acid, or iron-filings and acetic acid, nitrobenzol is converted into aniline or phenyl- arnine. C 6 H 5 (N0 2 ) + 3H 2 = 2H 2 -f C 6 H 5 (NH 2 ) Nitrobenzol. Aniline. When long heated with very concentrated nitric acid, nitro- benzol is transformed into metadinitrobenzol, C 6 H 4 (N0 2 ) 2 , which forms long, right rhombic prisms, fusible at 118. Azoxybenzol, Azobenzol, Hydrazobenzol, There are other products of the reduction of nitrobenzol, independently of aniline. When nitrobenzol is acted upon by alcoholic potas- sium hydrate, or by sodium amalgam in presence of water, the reduction is less complete, and it is converted successively into azoxybenzol and azobenzol (Zinin). 2C6H5-NQ2 + 3H2 = 3H2Q + Nitrobenzol. Azoxybenzol. 2C6H5-N0 2 + 4H2 = 4H2Q + ^ C6H5-N Nitrobenzol. Azobenzol. Azoxybenzol forms long, yellow prisms, fusible at 36, very soluble in alcohol and ether. Azobenzol forms large, red crystals, fusible at 66.5. It boils without decomposition at 293. It is insoluble in water, but dissolves in alcohol and ether. In the presence of reducing agents, such as hydrogen sul- phide, ammonium sulphide, or sodium amalgam and water, both of the preceding bodies fix hydrogen and are converted into hydrazobenzol. GYANOBENZOL PHENOL. 605 C6H5-N C6H5-N Azobenzol. Hydrazobenzol. The latter body crystallizes in tables, fusible at 131, almost insoluble in water but soluble in alcohol and ether. When submitted to dry distillation, it breaks up into azobenzol and aniline. 2C i2 H i2 N 2 = c i2 H l N 2 + 2C 6 H 5 .NH 2 Hydrazobenzol. Azobenzol. Aniline. CYANOBENZOL. (PHENYL CYANIDE, BENZONITRILE.) This body is formed in various reactions, particularly in the destructive distillation of hippuric acid, and by the dehydration of benzamide by phosphoric anhydride. C 6 H 5 -CO.NH 2 H 2 = C 6 H 5 -CN Benzamide. Benzonitrile. It is a colorless oil, which boils at 191. When heated with the alkalies, it yields benzoic acid and ammonia. C 6 H 5 -CN + 2H 2 = C 6 H 5 -C0 2 H + NH 3 Benzonitrile. Benzoic acid. PHENOL, OR PHENYL HYDRATE. This body bears the same relation to benzol that wood-spirit does to marsh gas. CH* CH 3 .OH Methane. Methyl hydrate. C6H 6 CPIP.OH Benzol. Phenol. It was discovered in coal-tar by Runge, who named it car- bolic acid. Laurent demonstrated that it plays the part of an alcohol. Indeed, it presents points of resemblance with the monatomic alcohols, but it differs from them by its acid char- acter, on account of which it is sometimes called phenic a,cid. Preparation. Large quantities of phenol are obtained from coal-tar, from which it is separated by distillation. That part which passes between 150 and 200 is collected apart and 51* 606 ELEMENTS OF MODERN CHEMISTRY. mixed with a saturated solution of potassium or sodium hy- drate to which solid potassa or soda is added. A crystalline phenate of potassium or sodium is formed ; it is dissolved in boiling water, the insoluble oil which floats is separated, and the alkaline solution is neutralized with hydrochloric acid. The phenol separates ; it is washed with a small quantity of water, dehydrated with calcium chloride, and rectified. The distilled product is cooled to 10, and the crystals which are deposited are allowed to drain out of contact with the air. Phenol may be made artificially from benzol by a process which is applicable to the preparation of all the phenols. It consists in treating benzol with fuming or even ordinary sulphuric acid. Phenylsulphurous acid is formed ; this is diluted with water to separate the excess of hydrocarbon, and the solution is neutralized with chalk ; calcium phenylsulphite, which is soluble, and sulphate, which is insoluble, are formed. The calcium phenylsulphite is converted into sodium phenyl- sulphite by double decomposition with sodium carbonate, and after evaporation and desiccation, the sodium phenylsulphite is fused in a silver crucible with an excess of potassium hydrate. The mass is exhausted with water, and the alkaline solution is decomposed by hydrochloric acid. The phenol separates and is dried and purified by distillation (Dusart, Wurtz, Kekule). The decomposition of sodium or potassium phenylsulphite is expressed in the following equation : C 6 H 5 .S0 3 K + KOH = C 6 H 5 .OH + K 2 S0 3 Potassium phenylsulphite. Phenol. Potassium sulphite. There is another very simple synthesis of phenol. In pres- ence of aluminium chloride, benzol absorbs oxygen directly and phenol is formed. C 6 H 6 + = C 6 H 6 O This reaction is one of the most unexpected and most in- teresting applications of a general method of synthesis discov- ered by Friedel and Crafts (see page 619). Properties of Phenol. Phenol is a solid, crystallizing in long, colorless needles, fusible at 35. It has a peculiar, char- acteristic odor, and an acrid, burning taste. It boils at 186. It is slightly soluble in water, but dissolves readily in concen- trated acetic acid. It possesses antiseptic properties. Although phenol is neutral to litmus-paper, it forms definite combinations with the alkalies. When it is mixed with a very TRINITROPHENOL. 607 concentrated solution of potassium hydrate, a crystalline mass is obtained which constitutes potassium phenate, C 6 H 5 .OK. Phosphorus perchloride converts it into phenyl chloride, identical with monochlorobenzol. C 6 H 5 .OH + PGP = C 6 H 5 C1 + POOP + HC1 Phenol. Phenyl chloride. The following remarkable reaction of phenol was first noticed by Reimer and Tiemann. When it is heated with chloroform and an excess of sodium hydrate, in the proportion of one molecule each of phenol and chloroform and four molecules of alkali, it is converted into salicylic aldehyde (salicyl hydride). C 6 H 5 .ONa + SNaOH + CHCP= C 7 H 5 2 Na -f 3NaCl + 2H 2 O Sodium Sodium salicylite. phenate. The compound C 7 H 5 2 Na is the sodium compound of sali- cylic aldehyde, into which it is converted by hydrochloric acid. TRINITROPHENOL. (PICRIC ACID.) C 6 H 2 (NO 2 ) 3 .OH When phenol is boiled with concentrated nitric acid, it is converted into trinitrophenol. C 6 H 5 .OH -f 3HN0 3 = 3H 2 + C 6 H 2 (N0 2 ) 3 .OH This body has long been known, and is generally called picric acid. It deposits from boiling water in lemon-yellow, crystal- line plates, only slightly soluble in cold water. Its taste is very bitter. With the bases it forms crystallizable salts, which deto- nate with violence when heated. Potassium pier ate, C 6 H 2 (N0 2 ) 3 .OK, crystallizes in long, yel- low needles, soluble in 14 parts of boiling water and in 250 parts at 15. It explodes violently when heated. Picramic Acid. When a current of hydrogen sulphide is passed through an alcoholic solution of picric acid saturated with ammonia, sulphur separates and the picric acid is con- verted into picramic acid (A. Girard). 3H 2 S = 2H 2 + S + CH 2 (NO 2 ) 2 (NH 2 )OH Picric acid. Picramic acid. The hydrogen sulphide partially reduces the picric acid, and one of the three groups (NO 2 ) is thus converted into a group 608 ELEMENTS OP MODERN CHEMISTRY. (NH 2 ). Picramic acid is dinitro-amido-phenol, that is, phenol in which two atoms of hydrogen are replaced by two groups (NO 2 ), and a third atom of hydrogen by the group NH 2 . When acetic acid is added to a hot aqueous solution of the ammonium salt of picramic acid, the picramic acid is deposited in fine red needles. AUKIN (ROSOLIC ACIDS). When 1 part of phenol is heated with 1 part of oxalic acid and 2 parts of sulphuric acid, it is converted into a color- ing-matter, which was first described under the name rosolic acid, or coralline-yellow. The same body or analogous bodies may be obtained by means of the rosanilines (see farther on). Indeed, it has been recognized that there are several homolo- gous bodies having the properties and the constitution of roso- lic acid. Rosolic acid made from pure phenol contains C 19 H 14 3 , and is called aurin (Dale and Schorlemmer). It occurs in very brilliant, red, anorthic prisms having a blue or green reflection. It corresponds to a rosaniline, C 19 H n (NH 2 ) 3 (pararosaniline). To ordinary rosaniline and its superior homologue, chrysoto- luidine (see farther on), correspond two other rosolic acids, supe- rior homologues of aurin. The following formulas indicate the relations which exist between these bodies: C lfl H"(OH) 3 C 19 H n (NH 2 ) 3 Aurin. Inferior homologue of rosaniline. C 20 H 13 (OH) 3 C 20 H 13 (NH 2 ) 3 Rosolic acid. Ordinary rosaniline. Aurin is used in dyeing. When it is heated to 180 with an alcoholic solution of ammonia, it is converted into a bright- red coloring matter, noticed by Persoz, and employed in dyeing under the name coralline-red. ANILINE, OR PHENYLAMINE. Aniline was discovered by Unverdorben among the products of the distillation of indigo, and was extracted from coal-tar by Runge. It is now prepared artificially by a process discovered by Zinin. This process consists in converting benzol into ni- ANILIDES. 609 trobenzol, and subjecting the latter to the action of reducing agents (see nitrobenzol). Iron and acetic acid are advantageously used to accomplish this reduction (Bechamp). Aniline is a colorless, mobile, highly-refracting liquid, having a peculiar, unpleasant smell, and an acrid, burning taste. It is a little heavier than water. It boils at 184.8. When ex- posed to the air, it becomes brown and is eventually resinified. "Aniline is almost insoluble in water, but mixes in all pro- portions with alcohol, ether, and the fatty and volatile oils. It does not restore the blue color to reddened litmus-paper, but nevertheless possesses the character of an alkaloid, for it forms well-defined salts with the acids. Reactions. 1. If a nitrate and sulphuric acid be added to aniline, a red color is produced. 2. If a few drops of aniline be poured into an excess of sul- phuric acid, and a small quantity of potassium dichromate be added, a magnificent blue color is developed, which changes to violet on the addition of water. 3. A solution of calcium hypochlorite (chloride of lime) added to aniline produces a beautiful violet tint. 4. When a solution of an aniline salt is heated with cupric chlorate, an intense black color is developed (Ch. Lauth). These reactions are applied in the arts in the preparation of coloring matters of incomparable richness. The most impor- tant of these matters is rosaniline, or fuchsine, which will be described farther on. Salts of Aniline. These are obtained by saturating aniline by the acids. Aniline liydrochloride, C 6 H 7 N.HC1, forms colorless needles, which are fusible, and can be distilled without alteration ; they are very soluble in water and in alcohol. Platinic chloride pre- cipitates from the solution fine yellow needles of a chloro-plati- nate, (^H'N.HCl/PtCl 4 . Aniline oxalate, (C 6 H 7 N) 2 C 2 H 2 4 , crystallizes from water in hard, thick prisms. When heated, it loses the elements of water, and is converted into oxanilide. ANILIDES. By the action of heat, the aniline salts lose the elements of water, and form compounds analogous to the amides, and which 2.Y* 610 ELEMENTS OF MODERN CHEMISTRY. Gerhardt named anilides. When aniline oxalate is heated, it is converted into oxanilide, which is no other than oxamide in which two atoms of hydrogen ara replaced by two phenyl groups, (C 6 H 5 ). C2Q2) C2Q2) H2 \ N2 (CH^2 ^2 H 2 J H 2 j Oxamide. Phenyl oxamide (oxanilide). H V N CH 5 N Hj HJ Acetamide. Pheny lace tarn ido (acetanilide.) DIAZOBENZOL COMPOUNDS. Nitrous acid exerts an energetic action upon aniline and the analogous bases ; it is indicated here because it presents a great generality and gives rise to remarkable bodies, which are called diazo-compounds. When a current of nitrous gas is passed into a saturated so- lution of an aniline salt, such as the nitrate, crystals of diazo- benzol nitrate are deposited. C 6 H 7 N.HN0 3 + HNO 2 = 2H 2 O + C 6 H 5 N 2 .N0 3 Aniline nitrate. Diazobenzol nitrate. This body is formed by the substitution of one atom of nitro- gen for three atoms of hydrogen in aniline nitrate. CH8-NH.HNO S aniline nitrate. CH 5 -N=N-(N0 3 ) diazobenzol nitrate. It forms long, colorless prisms, very soluble in water, slightly soluble in alcohol, and insoluble in ether. It explodes violently by heat or by percussion. This salt and its congeners present two remarkable reactions. When heated with water, they dis- engage nitrogen, and are converted into phenols. C e H 5 N 2 NO s ^_ H 2 = c*H 5 .OH -f N 2 + HNO 3 When they are boiled with absolute alcohol, they are reduced to hydrocarbons, nitrogen being disengaged and the alcohol being transformed into aldehyde. OTPN'.HSO* + C 2 H 6 = C 2 H 4 + C 6 H 6 + N 2 -f H 2 S0 4 Diazobenzol sulphate. Aldehyde. Benzol. When aniline is added to an aqueous solution of diazobenzol ROSANILINE. 611 nitrate, a diazo-compound is obtained which is more complex than the preceding and is called diazoamidobenzoL + NH 2 .C 6 H 5 = C 6 IP-N 2 -NH.C 6 H 5 + HNO 3 Diazobenzol nitrate. Aniline. DiazoamidobenzoL The same body is formed when a current of nitrogen tri- oxide is passed into a cooled alcoholic solution of aniline. It forms brilliant, golden-yellow scales, fusible at 91. It ex- plodes at a higher temperature. ROSANILINE AND ITS DERIVATIVES. This magnificent red coloring matter is obtained by heating aniline to 150 or 160 with arsenic acid, which acts in this case as an oxidizing agent. The solid product of the reaction is dissolved in water, and the filtered solution is treated with solu- tion of sodium hydrate ; the rosaniline which was combined with arsenic acid is precipitated. It is then dissolved in acetic or hydrochloric acid, and the salt so formed is crystallized. It separates in magnificent crystals which present a green re- flection, like the scales of cantharides, and dissolve in alcohol with a rich purple color. The rosaniline formed in this reaction results from the oxida- tion of the aniline, and toluidine (see farther on), which always exists in commercial aniline. C 6 H 7 N + 2C 7 H 9 N + O 3 = C 20 H 19 N 3 + 3H 2 Aniline. Toluidine. Rosaniline. In the preparation of rosaniline, arsenic acid, the use of which is dangerous, has been replaced by another oxidizing agent, which is nitrobenzol. The latter acts by virtue of the group NO 2 , which it contains (J. Persoz). This improvement has been introduced in France by Coupier, and in Germany by Meister, Lucius, Bruning. Properties of Rosaniline. The methods of preparation just indicated furnish the salts of rosaniline, such as the hydro- chloride, which is the rich coloring matter known as fuchsine. The free base is obtained by treating a hot, saturated solution of the hydrochloride with an excess of soda. The rosaniline separates as an almost colorless, crystalline precipitate. It is a triacid base which requires three molecules of hydrochloric 612 ELEMENTS OF MODERN CHEMISTRY. acid for its saturation. It is curious that free rosaniline is colorless and occurs in small crystals. The monohydrochloride of rosaniline, C 20 H 19 N 3 .HC1 (fuch- sine), forms dark-colored, rhombic tables, having a splendid green reflection. It is but slightly soluble in water, but dis- solves readily in alcohol, forming an intense purple solution. The trihydrochloride, C 20 H 19 N 3 .3HC1, forms yellow-brown needles which lose hydrochloric acid when heated or when dis- solved in water. Rosaniline and its salts present two important reactions : 1. When a salt of rosaniline is treated with reducing agents, such as nascent hydrogen (zinc and hydrochloric acid), the base fixes two atoms of hydrogen and is converted into leu- caniline, C 20 H 21 N 3 , a white powder slightly soluble in water. 2. By the action of nitrogen trioxide, rosaniline is converted into a diazo-derivative which yields rosolic acid when boiled with water (pages 608 and 610). Constitution of Rosaniline, According to Hofmann, the formula C 20 H I9 N 3 represents the composition of rosaniline. It is exact, but it has been recognized that the products known under the name fuchsine contain several isomerides (Rosen- stiehl), and it is known, besides, that there are several homo- logues of rosaniline. Without dwelling on the subject, we may mention the following bodies : C 19 H"N 3 pararosaniline (Fischer). C20fli9N 3 rosaniline. C 21 H 21 N 3 chrysotoluidine. There exist also corresponding leucanilines containing two more atoms of hydrogen. Hofmann has attributed to the rosaniline C 20 H 19 N 3 the con- stitution expressed by the formula 2(C 7 H 6 )" V N 3 H 3 j According to him, it is a triamine, containing at the same time a diatomic group phenylene, C 6 H*, and two diatomic groups C 7 H 6 . Recent researches tend to modify this view. E. and 0. Fischer consider that this rosaniline is a triamine, C 20 H 13 (NH 2 ) 3 , derived from a hydrocarbon C 20 H 16 , and that para- ROSANILINE. 613 rosaniline is a triamine, C 19 H n (NH 2 ) 3 , derived from a hydro- carbon, C 19 H U . By subjecting the corresponding leucanilines to the action of nitrous anhydride, and reducing the diazo- compounds thus formed by alcohol, these chemists obtained the hydrocarbons C 20 H 18 and C 19 H 16 , which were again con- verted into leucanilines, and then, by oxidation of the latter, into rosanilines. We may add that the hydrocarbon C 19 H 16 , which is solid and fusible at 93, is triphenylmethane, that is, marsh-gas, in which three atoms of hydrogen are replaced by three phenyl groups. CH 4 CH(C 6 H 5 ) 3 Methane. Triphenylmethane. Coloring Matters derived from Rosaniline. When rosan- iline is heated with ethyl iodide, three atoms of hydrogen are replaced by three ethyl groups, and this triethyl-rosamlme yields with the acids a magnificent violet color, known as Hof- mann's violet. Triphenyl-rosaniline, in which three atoms of hydrogen are replaced by three phenyl groups, C 6 H 5 , is formed when rosani- line is heated with an excess of aniline. This reaction, in which ammonia is disengaged, was discovered by Girard and de Laire. _|_ 3CTP.NH 2 = C 20 H 16 (C 6 H 5 ) 3 N 3 + 3NH 3 Rosaniline. Aniline. Triphenyl-rosaniline. The hydrochloride of triphenyl-rosaniline is of a magnificent blue color, and is known as Lyons blue (Ch. Girard and de Laire). The following formulae show the interesting relations which exist between rosaniline and its ethyl and phenyl deriv- atives : C 20 H 16 (C 2 H 5 ) 3 N 3 C 20 H 16 (C 6 H 5 ) 3 N 3 Rosanilhie. Triethyl-rosaniline. Triphenyl-rosaniline. (Base of Hofinann's violet.) (Base of Lyons blue.) We may mention among the derivatives of rosaniline, Paris violet and the aniline greens, particularly the beautiful color- ing matter known as night-green, because it retains its rich green tint in artificial light. Paris violet, which has been for some years manufactured by Poirrier, is a splendid color, produced by the oxidation of methylaniline or dimethylaniline. 52 614 ELEMENTS OP MODERN CHEMISTRY. CH3VN CH 8 >N HJ CH3J Methylaniline. Dimethylaniline. Ch. Lauth realizes this oxidation, or rather dehydrogena- tion, by heating methylaniline with cupric chloride. The reaction is complex, and, according to Hofmann and Martius, gives rise to trimethyl-rosaniline. When heated with methyl chloride, the base of Paris violet fixes two molecules of that compound, forming a combination of trimethyl-rosaniline and methyl chloride. This combination constitutes night-green. Dichlorometliylate of trimetliyl-rosauiline (night-green). DIPHENYLAMINE. CH5) CH5 I N HJ This body is derived from ammonia by the substitution of two phenyl groups for two atoms of hydrogen. It is formed in various reactions, of which the most interesting was discov- ered by Girard and de Laire. It consists in heating aniline hydrochloride to 256 with aniline. Ammonia is disengaged, and diphenylamine hydrochloride is formed. H N.HC1 + H N C6R5 N.HC1 + NR3 HJ Hj Hj Free diphenylamine forms crystals fusible at 54. It boils at 310. It is insoluble in water, but dissolves in alcohol, ether, benzol, and petroleum. Its odor recalls that of oil of rose. When heated with a mixture of oxalic and sulphuric acids, it yields a splendid blue color, soluble in water, and known as diphenylamine blue (Girard and de Laire). OXYPHENOLS. C6H6Q2 Three isomeric bodies having the composition C 6 H 6 2 O1T are known ; they are derived from benzol by the substitution of two hydroxyl groups for two atoms of hydro- RESORCIN. 615 gen. These three bodies are oxyphenol, or pyrocatechin, resor- cin, and hydroquinone. Pyrocatechin. This body is so named because it was first obtained by the destructive distillation of caoutchouc. It is also produced by the distillation of gum kino and various tan- nins which produce a green color with ferric salts. Pyroca- techin is a solid body, very soluble in water and alcohol, very slightly soluble in ether ; it crystallizes from its aqueous solu- tion in rectangular prisms, belonging to the orthorhombic sys- tem. It melts at 111.8, and sublimes below that temperature in brilliant, colorless plates. It boils between 240 and 245. Its odor is strong and excites sneezing. It has the character of an acid, like phenol itself. It dissolves in the alkalies and in the alkaline carbonates. When exposed to the air, these solutions become colored, first green, then brown and black. An aqueous solution of pyrocatechin produces a deep-green color with ferric chloride, which changes to dark-red on the addition of an alkali. Resorcin. This body, which is the homologue of orcin, C 7 H 8 2 , is formed when certain gums, such as galbanum, asafoetida, gum ammoniac, sagapenum, etc., are fused with potassium hydrate (Hlasiwetz and Earth). It is extracted from the fused mass by dissolving the latter in water, super- saturating with sulphuric acid, filtering, and agitating the fil- tered solution with ether, which dissolves the resorcin. After having driven off the ether on a water-bath, a residue is ob- tained which is distilled : the resorcin sublimes and condenses in radiated crystals. Oppenheim and Vogt obtained resorcin by fusing chloro- phenylsulphurous acid with potassium hydrate. The former body is obtained when chlorobenzol is treated with sulphuric acid. C 6 H5C1 + H'SO* = H2Q + Chlorobenzol. Chlorophenyl- sul jilinnius acid. C6H 4 CO. When isa- tin is heated with phosphorus pentachloride, hydrochloric acid is disengaged, and a chloro-compound is formed, and this by reduction yields indigo, PHTHALIC ACID. 637 XYLOLS AND DERIVATIVES. That portion of coal-tar which boils between 136 and 139 contains a mixture of isomeric hydrocarbons, which is desi^- CH 3 nated as xylol or xylene. It is dimethylbenzol, and can exist in three different isomeric modifications, like all of the di-substituted derivatives of benzol. Metaxylol, which boils at 137, predominates in the mixture of xylols which is obtained from coal-tar. When oxidized by chomic acid, it is converted into isophthalic acid, C 6 H 4 (C0 2 H) 2 . Orthoxylol is a colorless liquid, boiling at 140-141. Nitric acid oxidizes it to orthotoluic acid. Paraxylol is solid, and crystallizes in oblique rhombic prisms, fusible at 15. It boils at 136-137. Dilute nitric acid con- verts it into paratoluie acid. Chromic acid oxidizes it to ter- aphthalic acid. There are very many derivatives allied to these isomeric xylols. One or more atoms of hydrogen may be replaced, either in the benzol nucleus or in the methyl chains, by chlo- rine, bromine, or by groups such as OH, NO 2 , NH 2 , etc. The methyl chains may be oxidized by boiling the xylols with nitric or chromic acid, as indicated above. In this case the group CH 3 is replaced by the carboxyl group CO.OH, and the hy- drocarbons, C^H^CH 3 ) 2 , are converted into either toluic acids or phthalic acids, of each of which there are three isomerides. CO.OH CO.OH Xylols. Toluic acida. Phthalic acids. We cannot describe all of these bodies here, but must limit ourselves to a brief description of phthalic acid and its isomer- ides. PHTHALIC ACID. C 8 H0* = CH*(CO.OH) 2 Ordinary, or Orthophthalic Acid. Laurent obtained this acid by boiling naphthalene for a long time with nitric acid. It crystallizes in brilliant scales, or in short, thick prisms, which are but slightly soluble in cold water, very soluble in hot water, alcohol, and ether. It melts at 213, and loses the elements of water at a higher temperature, being converted into phthalic anhydride. 54 638 ELEMENTS OF MODERN CHEMISTRY. " 2 + <*0 Phthalic acid. Phthalic anhydride. Phthalic anhydride crystallizes in long, brilliant prisms, fusi- ble at 127-128. It boils at 277. It possesses a remarkable property, which was discovered by A. Baeyer, and which is now applied practically in the arts. When heated with the phenols, it combines with them directly with elimination of the elements of water, and compounds are obtained which are designated as phthaleins. Thus, when phthalic anhydride is heated with ordinary phenol, two molecules of phenol combine with one molecule of phthalic anhydride, with elimination of one molecule of water, and the phthalein of phenol is obtained. C6H5.0II . CO-CH*.OH Phthalic anhydride. 2 inol. phenol. Phthalein of phenol. When resorcin is heated with phthalic anhydride, two mol- ecules of water are eliminated, and a body is obtained to which Baeyer has given the name fluoresceiti. Phthalic anhydride. 2 mol. resorcin. Fluorescein. Fluorescein forms orange-red, crystalline grains, insoluble in cold water, and but slightly soluble in boiling water. It dis- solves readily in solutions of the alkalies and alkaline carbonates. Its dilute solutions are yellow, and have a magnificent green fluorescence. Hence the name fluorescein. Tetrabroino-fluorescein, C 20 H 8 Br 4 O 5 , is employed in dyeing under the name eosin. It communicates to silk a beautiful rose-red tint. Teraphthalic Acid (paraphthalic). Cailliot obtained this body by submitting oil of turpentine to a long ebullition with dilute nitric acid. The same acid is formed by the oxidation of paraxylol and its derivatives by potassium dichromate and sulphuric acid. It is a white powder, almost insoluble in water, alcohol, and ether. It sublimes without melting and without decomposition. Isophthalic Acid (metaphthalic) is formed by the oxidation of metaxylol. Long, thin, colorless crystals, slightly soluble in water, soluble in alcohol, and fusible above 300. It may be sublimed without decomposition. NAPHTHALENE. 639' NAPHTHALENE. This important compound was discovered by Garden in 1820, in coal-tar. Its composition was determined by Faraday, and its properties and transformations were principally studied by Laurent. It is a frequent product of the dry distillation of organic matters, and is formed in abundance when these matters, or the products of their decomposition, are heated to high tem- peratures. Thus it is formed in large quantities when tar is passed through red-hot tubes. Naphthalene is extracted from coal-tar, and is purified by crystallization in alcohol, or by sublimation. Properties. Naphthalene occurs in rhombic tables when it has been sublimed, and is deposited in prisms from its ethereal solution. It melts at 79.2, and boils at 218. It is inflam- mable, and burns with a very smoky flame. It is insoluble in water, slightly soluble in cold alcohol, freely soluble in boiling alcohol, and very soluble in ether. Nitric acid attacks naphthalene, forming nitro- derivatives, among which is nitre-naphthalene, C 10 H 7 (N0 2 ), which crystal- lizes in sulphur-yellow, rhombic prisms, fusible at 43. By long boiling with nitric acid, naphthalene is converted into phthalic acid, nitrophthalic acid, and oxalic acid. Chlorine acts on naphthalene in two ways : it combines di- rectly, forming chlorides of naphthalene, and produces numerous substitution products which generally combine with an excess of chlorine. Bromine yields only substitution compounds with naphtha- lene. Among all these products, we may mention the following : C 10 H8C1 2 naphthalene dichloride. C 10 H*C1 monochloronaphthalene. C 10 H 8 C1 4 naphthalene tetrachloride. C 10 H 6 C1 2 dichloronaphthalene. C 10 H 6 C1 2 C1 4 dichloronaphthalene tetra- C 10 H5C1 3 trichloronaphthalene. chloride. C 10 C1 8 C1 2 perchloronaphthalene di- C 10 C1 8 perchloronnphthalene. chloride. Concentrated sulphuric acid dissolves naphthalene, forming two acids : Naphtylsulphurous acid, C 10 H 7 .S0 3 H Naphtyldisulphurous acid, CRG J 640 ELEMENTS OP MODERN CHEMISTRY. The formation of the first of these acids is expressed in the following equation : C 10 H 8 + S0 4 H 2 = H 2 + C 10 H 7 .S0 3 H Naphthalene. Naphtylsulphurous acid. NAPHTOL. C 10 H 7 .OH This body is formed artificially by treating naphthalene with sulphuric acid, and fusing the naphtylsulphurous acid so ob- tained with potassium hydrate (see page 606). C 10 H 7 .S0 3 K + KOH == K 2 S0 3 + C 10 H 7 .OH Potassium naphtylsulphite. Naphtol. It forms silky needles or laminae, soluble in alcohol, ether, and benzol, almost insoluble in cold water, slightly soluble in boiling water. It m^lbs at 94. Its aqueous solution produces a violet color with chloride of lime. An isomeride of naphtol is known, /5-naphtol, fusible at 122, NAPHTYLAMINE. Zinin obtained this base in 1842 by reducing nitronaphtha- lene by ammonium sulphydrate, which may be advantageously replaced by iron and acetic acid. C 10 H 7 (N0 2 ) + 3H 2 = 2H 2 + C 10 H 7 (NH 2 ) Nitronaphthalene. Naphtylamine. It forms fine, colorless needles. It sublimes at a gentle heat, melts at 50, and boils without alteration at 300. It has a fetid odor. Its reaction is not alkaline, although it perfectly neutralizes the acids, with which it forms well-defined and crystallizable salts. When exposed to the air, the salts of naphtylamine acquire a violet color, probably due to an absorp- tion of oxygen. ANTHRACENE AND PHENANTHRENE. Anthracene, which is solid, exists in the less volatile pro- ducts of the distillation of coal-tar. It is obtained from the last products of this operation. The mass, which has a buttery consistence, is squeezed in a filter-press, and the residue is sub- ALIZARIN. 641 mitted to repeated distillations ; it is finally purified by com- pression and several crystallizations in benzol. Anthracene may be formed artificially by several processes, especially by passing the vapor of toluol and various derivatives of that body through a tube heated to bright redness. Under these conditions, two molecules of toluol lose six atoms of hy- drogen, and are converted into anthracene. C 6 H 5 -CH 3 2 C 6 JI*=CH 2 mol. toluol. Anthracene. In the pure state, anthracene forms rhombic tables, derived from an oblique rhombic prism. The crystals are colorless, and present a magnificent blue fluorescence (Fritzsche). They melt at 213, and distil without alteration at about 360. By the action of oxidizing agents, such as chromic acid, an- thracene is converted into a solid body, which crystallizes in beautiful yellow needles, fusible at 273, and which can be sublimed without alteration. It is anthraquinone^ C 14 H 8 2 , a body which bears the same relations to anthracene as quinone to benzol. Benzol. Anthracene. C 6 H 4Q2 C M H 8 Quinone. Anthraquinone. By treating anthraquinone with bromine, Graebe and Lieber- mann converted it into dibromanthraquinone, C u H 6 Br 2 2 , a solid body, which crystallizes in yellow needles. Fhenanthrene. Besides anthracene, there is another hydro- carbon of the same composition, which exists in coal-tar, and may also be formed artificially. It is called phenanthrene, and forms colorless scales, having a bluish fluorescence. It melts at 100, and boils at 340. It is soluble in 50 parts of alco- hol at 13 ; very soluble in hot alcohol, and in ether and benzol. ALIZARIN. Natural State and Synthesis. Alizarin is the name applied to the coloring matter of madder which llobiquet was the first to extract in a pure state. Graebe and Liebermann have re- cently made its synthesis by heating dibromanthraquinone to 200 with potassium hydrate. 54* 642 ELEMENTS OP MODERN CHEMISTRY. |_ 2KQH == 2KBr -f C 14 H 6 (OH) 2 2 Dibromanthraquinone. Alizarin. This reaction, slightly modified, has become within a few years the base of an important industry. Alizarin does not exist ready formed in the madder plant. The latter contains a glucoside to which Robiquet has given the name ruberythric acid, and which is decomposed by the action of acids into alizarin and glucose. CH0 M _|_ 2JJ2Q __ C H H 8 4 _|_ 2 C 6 H 12 () 6 Ruberythric acid. Alizarin. Glucose. Preparation, Alizarin may be extracted from madder by boiling the latter with a solution of alum. The filtered liquid, left to itself for some days, deposits impure alizarin as a brown- red precipitate, and holds in solution another coloring matter which is called purpurin. The precipitated alizarin is purified by washing with dilute hydrochloric acid, and crystallization in alcohol. The product thus obtained is exhausted with a boiling solution of alum, which removes the purpurin, and is finally dissolved in ether, which deposits it in crystals. To prepare artificial alizarin from anthracene, that hydro- carbon is first transformed into anthraquinone, and the latter body is treated with sulphuric acid to convert it into disulpho- anthraquinonic acid, which is then heated with an excess of potassium hydrate. C 14 H 6 (SO 3 K) 2 2 + 2KOH = C U H 6 (OH) 2 2 + 2K*SO S Potassium Alizarin. disulphoanthraquinonate. The alkaline mass is dissolved in water, precipitated by hy- drochloric acid, and the precipitate purified by crystallization in alcohol and finally by sublimation. The artificial product is delivered to commerce in the form of a paste, but the reaction by which it is formed produces, at the same time, isomerides which remain mixed with the aliza- rin, properly so called. Eight isomeric compounds are known having the composition C U H 8 0*. One of them, purpuroxan- thin, is contained in small quantity in madder. Properties of Alizarin Alizarin forms long, brilliant, orange-yellow prisms. It is scarcely soluble in cold water, but dissolves somewhat better in boiling water, and is soluble in alcohol, ether, and carbon-disulphide. Between 215 and 225, it sublimes in long, orange-yellow needles. It dissolves in sul- PURPURIN NATURAL ALKALOIDS, 643 phuric acid with a blood-red color, and water precipitates it without alteration from this solution. Boiling dilute nitric acid converts it into oxalic and phthalic acids. When alizarin is heated to redness with zinc powder, it is reduced to anthra- cene (Graebe and Liebermann). Alizarin forms combinations with the bases ; it dissolves in ammonia, with a purple color, and in the caustic alkalies, yield- ing purple solutions which have a blue reflection. Uses. Alizarin produces a red color on fabrics that are mor- danted with alumina, and a violet on those which are mor- danted with ferric oxide. It is the coloring principle of madder and of the commercial product known as garancin. The latter product is obtained by heating powdered madder with sulphu- ric acid to 100, and exhausting the mass with water. The residue is garancin. PURPURIN. This name is given to another coloring matter which may be extracted from madder, and which has already been mentioned. It appears to exist in the plant as a glucoside. It dissolves readily in alcohol and ether, with a red color. It crystallizes from weak alcohol in orange-colored needles, which contain one molecule of water of crystallization. From concentrated alcohol, it deposits in red, anhydrous needles. When heated, it melts and sublimes in red needles. Purpurin is an oxy alizarin, or a trioxyanthraquinone, C U H 5 (OH) 3 O 2 : indeed, it may be obtained by treating a solution of alizarin in concentrated sulphuric acid with an oxidizing agent, such as manganese dioxide (de Lalande). Inversely, the reduc- tion of purpurin reproduces alizarin (Rosenstiehl). It under- goes a complete reduction, and is converted into anthracene, when heated with zinc-dust. Independently of the purpurin just described, there are three other compounds isomeric with it. NATURAL ALKALOIDS. The alkaloids are nitrogenized substances capable of uniting with the acids, like ammonia, and forming with them definite combinations which constitute true salts. A large number 644 ELEMENTS OP MODERN CHEMISTRY. of these compounds can be formed artificially, and are derived directly from ammonia by the substitution of organic radicals for the hydrogen of that body. They are the compound, or substituted ammonias, and their constitutions are perfectly known. This is not, however, the case with the natural alka- loids, which have been discovered in many plants and vege- table products, and which often constitute the active principles to which these products owe their medicinal virtues. By anal- ogy, it may be inferred that these bodies also are derived from ammonia, like the compound ammonias. In 1806, the basic nature of one of the crystallizable princi- ples of opium was discovered by Serturner, but his discovery was unnoticed until 181*7, when he published it in a treatise on morphine. Among the more important discoveries in this class of compounds must be mentioned those of strychine, brucine, and especially quinine, discoveries which are due to Pelletier and Caventou (1820). All of the alkaloids contain nitrogen. They are divided into two classes, the first of which includes the liquid and volatile bases, and the second the solids. The latter generally contain oxygen, the former do not. The alkaloids possess one charac- teristic property which indicates their analogy with ammonia. With platinic chloride their hydrochlorides form double salts, which are sometimes insoluble in water, sometimes soluble and crystallizable. If a solution of platinic chloride be poured into a solution of quinine hydrochloride, a yellow precipitate is at once formed ; it is a combination of platinic chloride and quinine hydrochlo- ride, and is sometimes called quinine chloroplatinate, or platino- chloride. CONINE. This is a liquid and volatile alkaloid which is extracted from the hemlock ( Conium maculatum}. The seeds of this tree are crushed and distilled with sodium hydrate. The alkaline liquid which collects in the receiver is neutralized by dilute sulphu- ric acid, evaporated to a syrupy consistence, and the residue exhausted with a mixture of alcohol and ether, which dissolves the conine sulphate, and leaves ammonium sulphate. The alco- hol and ether are driven out by evaporation ; a concentrated NICOTINE. 645 solution of sodium hydrate is added to the conine sulphate, and the liquid is distilled. The conine passes with a certain quan- tity of water, on which it floats. It is separated, dried over some fragments of calcium chloride, and rectified in a vacuum. Conine is a limpid, oleaginous liquid, having a penetrating and nauseating odor, recalling that of hemlock. It boils at 168. It is slightly soluble in water, more so in cold than in hot water, so that a cold, saturated solution becomes clouded when heated. It is very soluble in alcohol and in ether. It has a strongly alkaline reaction, immediately restoring the blue color to reddened litmus-paper. It precipitates many metallic oxides from solutions of their salts. On contact with the air it becomes brown and resinified. Conine is often mixed with methylconine, a compound de- rived from conine by the substitution of a methyl group for an atom of hydrogen (Planta and Kekule). Wertheim has obtained from the flowers and seeds of the hemlock a solid alkaloid, which he has named conhydrine, C 8 H 17 NO, and which contains the elements of conine plus a molecule of water. Hugo Schiff has recently made the synthesis of an isomeride of conine, which he calls paraconine. NICOTINE. C 10 H 14 N 2 This alkaloid exists in tobacco. It may be obtained by ex- hausting tobacco with boiling water and evaporating the liquid to a syrupy consistence on a water-bath ; the still hot extract is then mixed with twice its volume of alcohol, allowed to settle, and the alcoholic liquid separated from the thick lower layer, which contains much calcium malate. The alcohol is distilled off, and the residue exhausted with strong alcohol, of which the greater part is then driven off by evaporation. Potassium hydrate is added to the alcoholic extract, which is then agitated with ether, which dissolves the nicotine set free. A few grammes of oxalic acid added to the ethereal solution causes the separa- tion of a syrupy deposit which contains oxalate of nicotine. This salt is decomposed by potassa, and the nicotine set free is dissolved out by ether. After the ether has been expelled on a water-bath, the nicotine is distilled in a current of hydrogen, that part being retained which passes above 180 (Schloesing). 646 ELEMENTS OP MODERN CHEMISTRY. Properties. Nicotine is a colorless liquid, having an offen- sive, penetrating odor. It rotates the plane of polarization to the left. It boils between 240 and 250, not, however, with- out undergoing partial decomposition. Above 146, it begins to distil slowly, and at 100 it emits white vapors ; at ordinary temperatures it gives off so much vapor that a rod wet with hydrochloric acid will be enveloped in white fumes if held a little distance above the nicotine. Nicotine dissolves in all proportions in water, alcohol, and ether. It has a strongly alkaline reaction, and perfectly neu- tralizes the acids, and precipitates the metallic oxides from solutions of their salts. It is one of the most violent poisons known. ALKALOIDS OF OPIUM. Opium is the thickened juice of the capsules of the white poppy (Papaver somniferum). It is obtained by making in- cisions in these capsules from the base to the summit. A milky juice exudes, and in the course of a day thickens and solidifies in tears. These are removed, pressed together, and fashioned into variously-formed masses. Opium contains a number of alkaloids combined with several acids. Among the latter are a syrupy acid, to which Ander- son gave the name thebolactic acid, but which has recently been recognized to be identical with lactic acid (Buchanan), and meconic acid, of which the composition is expressed by the formula C 7 H 4 7 . The latter is one of the more important constituents of opium ; it possesses the characteristic property of producing a blood-red color with ferric salts. Opium con- tains also a gummy matter, soluble in water, and a brown, in- soluble, resinous matter, which remains in the mass when opium is exhausted with water. The aqueous solution of opium has a brown color. The following alkaloids have been obtained from opium : Morphine C^H^NO 3 Codeine C^J^NO 3 Thebaine C 19 H 21 N0 3 Papaverine C^H^NO* Narcotine C 22 H 23 N0 7 Narceine C 23 H 29 N0 9 Besides these, Merck has described another alkaloid of opium under the name porphyroxine ; but, according to Hesse, this MORPHINE. 647 body is a mixture of several bases, to which he has given the names meconidine, laudanine, codamine, and lanthopine. Opium sometimes contains an alkaloid which is designated as pseudomachine, and which is oxymorphine, C 17 H 19 NO 4 . Independently of these alkaloids, a neutral, crystallizable substance has been extracted from opium, and called meconine, C 10 H 10 4 . Of all these bodies, we will only consider morphine, codeine, and narcotine. MORPHINE. C"H 19 NO 3 + H 2 O Preparation. 1. Opium is cut into slices and exhausted with water. The solution is evaporated to a syrupy consistence and the still hot extract is mixed with an excess of pulverized sodium carbonate. After the lapse of twenty-four hours, the precipitate is collected and exhausted with dilute acetic acid, which dissolves the morphine and leaves the narcotine. The liquid is filtered, decolorized by animal charcoal, and super- saturated with ammonia. The morphine is precipitated, and is purified by crystallization in alcohol (Merck). 2. One kilogramme of opium is exhausted with cold water ; 100 grammes of pure lime are added to the liquid, which is then evaporated to a syrupy consistence at a temperature of 65 or 75. After cooling, the mass is exhausted with 3 litres of water which leaves the meconate of calcium ; the latter is separated by filtration. The liquid is then evaporated to one- fourth its volume, and while it is still hot, 50 grammes of calcium chloride dissolved in 100 grammes of water and 8 grammes of hydrochloric acid are added. This mixture is left to itself for about two weeks, when it will be found to have set in a mass of crystals which are bathed in a colored mother-liquor. The deposit is pressed in a cloth, dissolved in boiling water, with addition of animal charcoal, and the solution filtered. On cooling, a mass of crystals ia formed, consisting of a mixture of morphine hydrochloride and codeine hydrochloride. These are pressed, dissolved in water, and ammonia is added, which precipitates the greater portion of the morphine, while the codeine remains in solution. The deposit is collected on a filter and redissolved in boiling alcohol, from which the morphine crystallizes on cooling (Robertson and Gregory). 648 ELEMENTS OF MODERN CHEMISTRY. Properties. Morphine crystallizes in small, colorless, right rhombic prisms, having a bitter taste. It is insoluble in ether, in chloroform, and in benzol. The alcoholic solution rotates the plane of polarization to the left. The crystals contain one molecule of water which they lose at 100. Morphine dis- solves easily in a solution of potassium hydrate ; it is very slightly soluble in ammonia ; almost insoluble in water. Tests. 1. If a few drops of a solution of iodic acid be added to an alcoholic solution of morphine, the liquid immediately assumes a brown or yellow color, due to the liberation of iodine. Iodic acid exerts an oxidizing action on morphine. 2. If a small quantity of morphine in powder be added to a solution of ferric chloride, a blue color is produced. 3. Nitric acid produces an orange-red color with morphine. The last two reactions are characteristic. When morphine is heated to 200 with potassium hydrate, it disengages methylamine. Morphine Hydrochloride. This salt, of which the prepara- tion has already been indicated, crystallizes in silky needles, soluble in 1 part of boiling and 16 or 20 parts of cold water; it is very soluble in alcohol. The crystals contain C 17 H 19 N0 3 . HC1 -f 3H 2 0. Platinic chloride forms a yellow precipitate of a double chlo- ride in an aqueous solution of morphine hydrochloride. (C 17 H 19 N0 3 .HCl) 2 .PtCl 4 Hydrochloride of morphine is much used in medicine. When its solution is heated to 60 with silver nitrite, the base is oxidized and converted into oxymorphine, C 17 H 19 NO 4 . When morphine is heated to about 140 with concentrated hydrochloric acid, it is transformed into a new base, apomor- phine, C 17 H 17 NO 2 , derived from morphine by the removal of one molecule of water (Matthiessen). This base possesses special therapeutic properties. When administered by hypo- dermic injection or swallowed, it acts as an emetic. CODEINE. C 18 H 21 NO + H 2 O Codeine is methylmorphine. It is obtained from the am- moniacal mother-liquor from which the morphine is deposited, in the preparation of the latter body by the process of Robert- NARCOTINE. 649 son and Gregory. For this purpose, the mother-liquor is con- centrated and caustic potassa is added, which precipitates the codeine. It is collected, dissolved in hydrochloric acid, the solution decolorized with animal charcoal, and the codeine again precipitated by potassa. Lastly, the precipitate is dissolved in ordinary ether, which deposits the codeine in voluminous crys- tals by spontaneous evaporation. These crystals are right rhombic prisms, and contain one molecule of water. Anhydrous ether deposits codeine in anhy- drous rectangular octahedra. Codeine dissolves in 89 parts of water at 15, and is more soluble in boiling water. Alcohol and ether dissolve it readily, and the alcoholic solution rotates the plane of polarization to the left. If bromine-water be poured upon codeine in fine powder, the latter dissolves, and is converted into hydrobromide of monobromo-codeine. By the continued addition of bromine- water, a yellow precipitate is formed, consisting of hydrobro- mide of tribromo-codeine, that is, codeine in which three atoms of hydrogen are replaced by three atoms of bromine. NARCOTINE. Narcotine may be extracted from the residue of opium which has been exhausted by water. This is treated with hydrochloric acid, filtered, and the filtrate precipitated by sodium carbon- ate. The precipitate is dissolved in alcohol, and the alcoholic solution decolorized by animal charcoal. The narcotine crys- tallizes out on cooling. It forms brilliant, colorless prisms, belonging to the system of the right rhombic prism. It melts at 70. It is insoluble in cold water, and requires for its solution about 60 parts of cold absolute alcohol, or 12 parts of boiling absolute alcohol. It is soluble in ether, a character which distinguishes it from mor- phine. Its alcoholic and ethereal solutions have a bitter taste, and turn the plane of polarization to the left. If a few crystals of narcotine in a watch-glass be moistened with sulphuric acid containing a trace of nitric acid, an intense blood-red color is produced. By the action of certain oxidizing agents, narcotine is de- 2c 55 650 ELEMENTS OF MODERN CHEMISTRY. composed into a new alkaloid, cotarnine, and an acid which is called opianic acid (Wbhler). C -r2 H 23 NO T + o = ciogiops _|_ C 12 H 13 N0 3 Narcotine. Opianic acid. Cotarnine. Cotarnine crystallizes in colorless, silky needles, grouped in stars. When subjected to the action of hydriodic acid, narcotine loses successively three methyl groups, and yields hydriodides of three new bases. One of them contains C 19 H 17 NO T , and has been designated as nornarcotine or normal narcotine. It is formed according to the equation C 22 H 23 N0 7 + SHI = C 19 H 17 N0 7 + 3CIPI Narcotine. Nornarcotine. Methyl iodide. Hence narcotine itself represents trimethy I - nornarcotine, C 19 H H (CH 3 ) 3 N0 7 (Matthiessen and Foster). " The intermediate terms between narcotine and nornarcotine are also known, ALKALOIDS OF CINCHONA. The different cinchona barks owe their febrifuge virtues to several alkaloids, of which the more important, quinine and cin- chonine, were discovered by Pelletier and Caventou in 1820. Since then, quinidine and cinchonidine have been isolated, the first isomeric with quinine, the second with cinchonine. All of these are crystallizable alkaloids. When their sulphates are heated with sulphuric acid, they are converted into two new isomerides, quinicine and cinchonicine. The latter are not crys- tallizable. Hence the following six alkaloids are known : Cinchonine, cinchonidine, cinchonicine . . Quinine, quinidine, quinicine These alkaloids are by no means distributed in the same manner in the numerous species and varieties of cinchona bark, and these barks are not equally rich in alkaloids. The follow- ing summary gives some indications of this difference : 1 KILOGRAMME OF BARK TIELDS : QUININE SULPHATE. "uL^HATE? Yellow bark (Cinchona Calisaya) . . 30-32 grammes. 6-8 grammes. Red bark (Cinchona snccirubra) . . . 20-25 " 8 " ("Loxa (Cinchona condami- Pale bark \ nea) ....... 8 " 6 (Huanuco (Cinchona nitida) 6 " 12 " QUININE. 651 In the cinchonas, these alkaloids are combined with a well- defined, crystallizable acid, whose composition is expressed by the formula C 7 H 12 6 . It is quinic acid. This acid is obtained from the calcium quinate which is de- posited in a few days, when the liquid separated from the quino- calcium precipitate is concentrated and allowed to stand (see farther on). This calcium quinate is purified by several crystallizations, and its solution decomposed by oxalic acid. The quinic acid remains in the solution, and separates in crystals when the liquid is properly concentrated. Quinic acid crystallizes in beautiful, transparent, oblique rhombic prisms. It is very soluble in water, and but slightly soluble in absolute alcohol. It melts at 161.5, losing at the same time the elements of water. Its aqueous solution rotates the plane of polarization to the left. Its composition corresponds to the formula C 7 H 12 6 . When distilled with a mixture of sulphuric acid and manganese diox- ide, it yields quinone, C 6 H 4 2 . A substance is also found in cinchona bark which is called quinotannic acid. It belongs to the tannin group, and is a glucoside. Hlasiwetz states that it can be decomposed into glucose and cinchonine red, a substance noticed by Pelletier and Caventou as produced during the preparation of quinine. QUININE. C 2 H 2 *N 2 O 2 When ammonia is added to a solution of sulphate of quinine, a white precipitate of quinine is obtained, which, when left to itself and moistened with water from time to time, becomes crystalline by combining with one molecule of water. Quinine is very bitter. It dissolves in 2266 parts of cold, and in 760 parts of boiling water ; in 1.33 parts of cold alco- hol, and 22.6 parts of ether (J. Regnauld). It is also soluble in chloroform. Its alcoholic solution turns the plane of polar- ization to the left. When water at 32 is added to the hot alcoholic solution until a cloud begins to form, resinous quinine is deposited, and also colorless, prismatic crystals containing three molecules of water. Quinine Sulphate, 2(C 20 H 2 *N 2 2 ).S0 4 H 2 + 8H 2 0. Prep- 652 ELEMENTS OF MODERN CHEMISTRY. ration. This salt, which is extensively used in medicine, is prepared by boiling yellow bark (Cinchona Calisaya] or red bark (Cinchona succirubrd) with water acidulated with sul- phuric or hydrochloric acid. A slight excess of milk of lime is then added in small quantities to the decoction, and precip- itates not only the quinine and cinchonine, but all of the color- ing matter (cinchonine red), which forms an insoluble com- pound with the lime. The quinic acid remains in solution as calcium quinate. The quino-calcium deposit contains also the excess of lime, and calcium sulphate, in case sulphuric acid has been employed. It is collected on a cloth, allowed to drain, pressed, and dried. It is then exhausted with boiling alcohol, which dissolves out the alkaloids. The alcoholic solution, concentrated by distillation, deposits the cinchonine in crystals, in case the bark employed be rich in that alkaloid. The mother-liquor retains the quinine. It is neutralized by sulphuric acid, and the alcohol distilled off. The quinine sulphate crystallizes in a mass on cooling, and is purified by redissolving it in boiling water and adding animal charcoal. It has been proposed to replace the alcohol, in the extrac- tion of the quino-calcium deposit, by certain fixed or volatile oils, which dissolve quinine. For this purpose, petroleum and the heavy oils produced by the distillation of tar, and which are abundant in commerce, may be used with advantage. After having dissolved the alkaloids in these oils, the solutions are agitated with dilute sulphuric acid, which removes from them the quinine and cinchonine. Sulphates are thus obtained which may be crystallized. Properties. Quinine sulphate occurs in long, thin, light needles, which are somewhat flexible. It requires for its solu- tion 740 parts of water at 13, or about 30 parts of boiling water. The solution restores the blue color to reddened litmus- paper. It turns the plane of polarization to the left (Bouchar- dat). When crystallized in alcohol, quinine sulphate contains only two molecules of water. If some quinine sulphate be suspended in cold water, and a few drops of sulphuric acid be added, the sulphate dissolves and the liquid acquires a blue fluorescence. In this case, quinine sulphate, which is a basic salt, is con- verted into a salt, C'^H^OISO 4 !! 2 , which has an acid reac- tion, and is called quinine acid sulphate. This salt crystallizes CINCHONINE. 653 with 7 molecules of water. A still more acid sulphate is known, C"H 14 N*O I .(SO t H 8 ) 1 -f m 2 0. If an excess of chlorine-water be added to a solution of quinine sulphate, and the liquid be supersaturated with ammo- nia, a beautiful green color will be produced. This reaction is characteristic of quinine. When tincture of iodine is added to a solution of quinine sulphate in hot acetic acid, in a few hours the liquid deposits large, thin plates. It is iodoquinine sulphate, C 20 H 24 N 2 2 F. S0 4 H 2 -f 5IFO (Herapath). These crystals appear green by reflected light, and are almost colorless by transmitted light. When two of them are crossed, the portions which are superposed almost entirely intercept the passage of light. In this respect, iodoquinine sulphate acts as a polarizer, like tourmaline. Uses. Quinine sulphate is a valuable remedy. It is prin- cipally employed as a febrifuge, and generally in the treatment of diseases of an intermittent type. It is successfully admin- istered in other diseases, especially in acute articular rheuma- tism, gout, certain neuralgias, etc. CINCHONINE. Cinchonine is obtained as an accessory product in the manu- facture of quinine. It deposits from its alcoholic solution in brilliant, colorless, quadrilateral prisms. It is insoluble in water, but soluble in alcohol and chloroform. It is almost insoluble in ether, a property which distinguishes it from qui- nine. Its alcoholic solution turns the plane of polarization to the right. Cinchonine has a bitter taste. It melts at 1*70, and when cautiously heated in the bottom of a closed tube, it partly sub- limes in very light, delicate crystals. When treated with a dilute solution of potassium permanganate, it forms various substitution products, and a new base remains, less oxidizable than cinchonine. It is hydrocinchonine. Caventou and Willm consider that this base is contained, in the state of mixture, in commercial cinchonine. By oxidizing cinchonine with nitric acid, Weidel has ob- tained a series of acids, one of which contains nine atoms of carbon ; it is quinolic acid, C 9 H 6 N 2 4 , while two others contain 654 ELEMENTS OF MODERN CHEMISTRY. each eleven atoms. Lastly, the fourth of these acids, cinchonic. acid, has the composition C 20 H W N 2 4 . When distilled, it yields a non-nitrogenized acid, C 10 H 10 5 , pyrocinchonic acid, which is an isomeride of opianic acid. STRYCHNINE AND BRUCINE. Pelletier and Caventou discovered these two alkaloids in various vegetable products derived from plants belonging to the genus Strychnos, such as nux vomica (seeds of the Strychnos Nux vomica), false angustura bark, which comes from the same Strychnos, Saint Ignatius bean (seeds of the Strychnos Ignatii}, etc. These alkaloids, to which igasurine has recently been added (Desnoix), appear to be combined in the Strychnos with an acid but little known, which Pelletier and Caventou called iaasuric acid. Strychnine, C M H B N 2 0*. Preparation. Strychnine is ex- tracted from nux vomica by a process analogous to that which serves for the preparation of quinine. The crude strychnine which deposits in crystals from its alcoholic solution is always mixed with brucine.. The two alkaloids are separated by con- verting them into nitrates, which are made to crystallize ; the strychnine nitrate, less soluble than that of brucine, deposits in needles, and the concentrated solution afterwards deposits voluminous crystals of brucine nitrate. To isolate the alka- loids, the corresponding nitrates are precipitated by ammonia, and the alkaloid dissolved in boiling alcohol, which deposits it in crystals on cooling. Properties. Strychnine crystallizes in rectangular octa- hedra, sometimes in quadrilateral prisms terminated by four- sided pyramids. It is colorless and odorless, but extremely bitter. It is insoluble in water and in ether, and scarcely soluble in absolute alcohol. It dissolves readily in ordinary alcohol, in chloroform, and in the volatile oils. Its alcoholic solution turns the plane of polarization to the left. Strychnine is one of the most active poisons known ; even in very small doses it produces violent tetanic spasms. Brucine, C 23 H 26 N 2 4 -f 4H 2 0. Brucine, separated from strychnine by the process above indicated, crystallizes by slow evaporation of its solution in weak alcohol in oblique rhombic prisms, which are often quite large. These crystals, which contain four molecules of water, rapidly effloresce in the air. COCAINE ACONITINE. 655 Brucine is almost insoluble in water, but dissolves readily in alcohol and very slightly in ether. The alcoholic solution ro- tates the plane of polarization to the left. If brucine be moistened with nitric acid, it immediately assumes a blood-red color and, by the aid of a gentle heat, disengages carbon dioxide and vapors which contain methyl nitrite (Strecker). COCAINE. Cocaine was obtained by Niemann from coca leaves (Ery- ihroxylon Coed]. It has been studied by Wohler and Lassen. Preparation. Coca leaves are exhausted several times with water at a temperature between 60 and 80, and the solu- tion is precipitated by lead acetate, and filtered ; the filtered solution is freed from excess of lead acetate by addition of sodium sulphate and then, after a new filtration, the solution is evaporated. Sodium carbonate is then added until it pro- duces a faint alkaline reaction ; the liquid is lastly agitated with ether, which takes up the cocaine and leaves it on evapo- ration. Properties. Cocaine crystallizes in oblique rhombic prisms of four or six sides, which are colorless and odorless, and fuse at 98. It is but slightly soluble in cold water, more soluble in alcohol, very soluble in ether. Its taste is bitter, its reaction slightly alkaline. When heated with hydrochloric acid, it ab- sorbs two molecules of water and decomposes into methyl alco- hol, benzoic acid, and a crystallizable base, ecgonine. C 9 H 15 N0 3 -f H 2 0. C n H 2i N0 4 _j_ 2H 2 = CH 15 N0 3 + CH 4 -f C 7 H 6 2 ACONITINE. The Aconitum Napellm contains, independently of aconitic acid, a base which was extracted by Geiger and Hesse. It occurs as a white powder, or as colorless, tabular crystals, only slightly soluble in water, very soluble in alcohol. Its taste is acrid and bitter. It is a violent poison. Its nitrate crystal- tizes readily. v 656 ELEMENTS OF MODERN CHEMISTRY. ATROPINE. This alkaloid, which is largely used in the treatment of dis- eases of the eyes, was discovered in 1833 by Geiger and Hesse, and by Mein, in the belladonna, or deadly nightshade (Atropa Belladonna). Planta has shown the identity of atropine and daturine, which has been obtained from the thorn-apple (Datura Stramonium). Preparation. Belladonna-root is reduced to powder and digested several days with alcohol. The solution is filtered, slaked lime, in quantity equal to one-twentieth of the weight of root employed, is added, the solution again filtered, and rendered slightly acid with sulphuric acid. It is again filtered, and f of the alcohol distilled off. The residue is concentrated at a gentle heat, and a concentrated solution of potassium carbonate is added until the liquid, now neutral, begins to be clouded. After a few hours, the precipitate is separated by filtration, and potassium carbonate is added to the filtrate as long as impure atropine is precipitated. The next day, the deposit is collected on a filter, pressed, dried, and exhausted with 96 per cent, alcohol. The solution is decolorized with animal charcoal, the liquid diluted with five or six times its volume of water and put in a cool, dark place. The atropine is deposited in 12 or 24 hours in crystalline needles. Properties. Atropine crystallizes in delicate needles, fusi- ble at 90. It dissolves in 300 parts of cold water, and in almost all proportions of alcohol. It is less soluble in ether. At 140 it volatilizes, but the greater part of it is decomposed. In burning, atropine diffuses the odor of benzoic acid. When it is treated with potassium dichromate and sulphuric acid, benzyl aldehyde distils and benzoic acid is formed (Pfeiffer). Atropine is a virulent poison. A solution of sulphate of atropine is used in medicine. A single drop, even of a very dilute solution of this salt, produces dilatation of the pupil. THEOBROMINE. Theobromine exists in the beans of the cacao ( Theobroma Cacao). To prepare it, the crushed cacao beans are exhausted CAFFEINE ALBUMINOID MATTERS. 65*7 with water, and the aqueous extract is precipitated by lead ace- tate. The precipitate is separated by filtration, and the filtrate is freed from an excess of lead by hydrogen sulphide ; it is then again filtered, and evaporated to dryness. The residue is dis- solved in absolute alcohol and the solution concentrated ; the theobromine separates as a crystalline powder, having a bitter taste, slightly soluble in alcohol and ether. It may be sublimed. It is soluble in ammonia. CAFFEINE, OR THEINE. H*0 Caffeine was extracted from coffee in 1821 by Pelletier and Caventou, and by Robiquet and Runge. Liebig, Pfaff, and Wohler determined its composition. It exists in coffee, tea, Paraguay tea (leaf of the Ilex Paragnaiensis^ and guarana (seeds of the Paidlinia Sorbilis}. The latter product contains 5 per cent. Caffeine is methyl-theobrouiine. Preparation. Caffeine, or theine, is generally obtained from tea. Powdered tea is exhausted several times with cold alcohol, and the tincture is precipitated by subacetate of lead, filtered, and a current of hydrogen sulphide passed through the filtrate to precipitate the excess of lead. The filtered liquid is then evaporated to one-fourth its volume, neutralized by po- tassium hydrate, and allowed to crystallize (Herzog). Properties. Caffeine forms long, silky needles, which are light and colorless. It loses its water of crystallization at 100, melts at 178, and sublimes without alteration at a higher tem- perature. It is only slightly soluble in cold water, but dissolves readily in boiling water, and in alcohol. It is but slightly soluble in ether. It forms definite combinations with the acids. When boiled with concentrated potassa, it disengages methylamine. When caffeine is boiled for a few minutes with fuming nitric acid, the yellow liquid evaporated to dryness, and the residue moistened with ammonia, a purple color is produced, analogous to that of murexide. ALBUMINOID MATTERS. The albuminoid matters are complex organic substances, con- taining carbon, hydrogen, oxygen, and nitrogen, which are often associated with a small proportion of sulphur. By their com- 658 ELEMENTS OP MODERN CHEMISTRY. position and properties they are allied to the coagulable matter which exists in white of egg and in the serum of blood, and which is called albumen. The epidermic productions and the insoluble substances which are converted into gelatin or chondrin by boiling, differ from albumen and its allied compounds by their composition. They contain less carbon and more nitrogen. For this reason the neutral nitrogenized matters of the economy are divided into two comprehensive classes, albuminoid substances proper, and those substances which resemble in composition the insol- uble matter which forms the cartilage of bones, and which yield gelatin by the action of boiling water. The more important of the albuminoid bodies are as follows : Albumen ... A nitrogenized matter, coagulable by heat, and exist- ing in many liquids of the animal economy, particu- larly in white of egg and the serum of blood. Fibrin .... A nitrogenized matter, which deposits in the solid state during the coagulation of blood. Casein .... A nitrogenized matter, existing in milk, and considered identical with albuminate of sodium. Globulin ... An albuminoid substance that can be obtained from the red blood-corpuscles. Syntonin . . . An albuminoid substance, resulting from the action of very dilute hydrochloric acid on muscular fibres. Myosin .... An albuminoid body contained in muscular fibres. Vitellin .... The albuminoid matter of yolk of egg. Hemoglobin . . A crystallizable substance contained in red blood-cor- puscles. Among the cartilaginous and gelatinous substances are the following : O^sein, or collagene, which forms the cartilage of bones, and yields gelatin when boiled with water. Chondrogin, which constitutes the cartilage of the short ribs, and which yields chondrin when boiled with water. Keratin, or horny structure. Elastin, the constituent of elastic tissue. Fibroin, a product peculiar to silk-worms, etc. The substances belonging to these two groups possess the following elementary composition : FIRST GROUP. SECOND GROUP. Carbon 53.5 50.0 Hydrogen 6.9 6.6 Nitrogen 15.6 16.8 Oxygen 23 to 22.4 26.1 to 23.1 Sulphur 1 to 1.6 0.5 to 3.5 100.0 100.0 ALBUMINOID MATTERS. 659 Of most of the albuminoid substances, two modifications are known, one soluble and the other insoluble. Thus heat, acids, and alcohol convert soluble albumen into insoluble albu- men, and the latter appears to have the same, or very nearly the same composition after coagulation as before. The insoluble albuminoid bodies, such as coagulated albu- men, cooked albumen, fibrin, and casein, dissolve by the aid of a gentle heat in potassium hydrate, to which they yield a portion of their sulphur. The alkaline liquid, supersatu- rated with acetic acid, precipitates the dissolved matter in flakes. Concentrated and boiling solutions of the alkalies decompose all albuminoid substances, the principal products of the decom- position being carbon dioxide, formic acid, gtycocol, and its homologue leucine, C 6 H 13 N0 2 , as well as a nitrogenized sub- stance known as tyrosine and containing C 9 H n N0 3 . The other decomposition products will be indicated when treating of albumen. Leucine and tyrosine are also formed when albuminoid sub- stances are long boiled with dilute sulphuric acid. At the same time, aspartic acid, and glutamic acid, C 5 H 9 N0 4 , which is the acid amide of normal pyrotartaric acid, is formed. ^. < C0 2 H Pyrotartaric acid. Glutamic acid. Concentrated hydrochloric acid dissolves the insoluble albumi- noid bodies, and the solution assumes a violet color, especially on contact with the air (Caventou). When brought into contact with water containing one or two thousandths of hydrochloric acid, insoluble albuminoid mat- ters swell up and are finally converted into a transparent jelly, which partially dissolves in water. By the action of energetic oxidizing agents, such as chromic acid, or manganese dioxide and sulphuric acid, albuminoid bodies produce various products of Oxidation and decomposi- tion, among which we may note particularly: (1), the volatile acids of the series, C n H 2n 2 , from formic acid to caproic acid inclusive ; (2), the corresponding aldehydes ; (3), the nitriles (hydrocyanic ethers), propionitrile (ethyl cyanide), and valero- nitrile (butyl cyanide) ; (4), benzoic acid and benzyl alde- hyde. 660 ELEMENTS OP MODERN CHEMISTRY. ALBUMEN. Two modifications of albumen are known : one is soluble, the other insoluble. Soluble albumen exists in solution in white of egg, and in other liquids of the animal economy. The coagulable prin- ciple of the serum of blood is a liquid very analogous to the albumen of white of egg ; some chemists have called it serin. When a filtered solution of white of egg is evaporated at a low temperature or in a vacuum, the soluble albumen at length dries to a transparent, yellowish mass, having a gummy appear- ance. In this state it is not pure ; it remains combined with a trace of alkali and mixed with a small quantity of salts. When treated with water, it again dissolves. When it is per- fectly dry, it may be heated to even 1 00 without losing all of its water. The greater part, if not all, of the salts which exist in white of egg with the albumen may be removed by dialysis (Graham). When a solution of white of egg or of the serum of blood is heated, the liquid begins to be clouded at 70, and coagulates at about 73, sometimes in flakes, sometimes in a white mass, according to the concentration of the solution ; heat converts albumen into the insoluble variety. When white of egg is diluted with eight or nine times its volume of water and the carbonic acid gas which is dissolved or combined with the albumen is carefully expelled at a low temperature, a solution is obtained which is not coagulable by heat. The lost property may, however, be restored by passing carbon dioxide through the liquid. It is generally considered that there is no difference of com- position between soluble and insoluble albumen. However, Schiitzenberger finds that the difference is sensible. If strong alcohol be added to a solution of albumen, a white coagulum is formed, which becomes insoluble in water by the prolonged action of alcohol. Action of Acids on Albumen. Sulphuric, hydrochloric, and nitric acids precipitate albumen in thick flakes, which retain a certain quantity of acid ; the latter may be removed by pro- longed washings with water. The action of nitric acid upon albumen is often used for the detection of that substance in pathological urine. A still more ALBUMEN. 661 sensitive reagent is metaposphoric acid, which precipitates the smallest traces of albumen contained in a solution. Ordinary phosphoric acid, acetic acid, and lactic acid, do not precipitate solutions of albumen. Action of Alkalies on Albumen. When white of egg is beaten up with a few drops of a very concentrated solution of potassium hydrate, it sets in a few minutes in a soft, trans- parent, semi-solid mass, from which the excess of potassa may be removed by washing with cold water. The residue is albu- minate of potassa, from which all of the excess of potassa may be removed by prolonged washings. This gelatinous albumi- nate of potassa dissolves in boiling water. Acetic acid precip- itates the albumen from the solution. When potassa is added to a solution of albumen, albuminate of potassa is formed in the same manner ; acetic acid precip- itates the albumen, which it renders insoluble, but the alkaline solution is not troubled by boiling. If a few drops of lead acetate be added to the liquid, the oxide of lead formed will remain dissolved in the excess of alkali, 'the liquid then blackens on boiling, for the sulphur contained in the albumen acts on the lead, forming lead sulphide. Insoluble albumen dissolves in the alkalies and alkaline car- bonates, forming albuminates. Albumen combines with calcium hydrate, as with potassa ; a mixture of white of egg and slaked lime constitutes a very hard cement. By subjecting albumen and its analogues to the action of an aqueous solution of barium hydrate at a temperature of 140 or 150, Schiitzenberger observed that these bodies decompose, by hydration, into ammonia, carbon dioxide, oxalic, sulphurous, and acetic acids (the latter three bodies in very small propor- tion), and into other products, which are mostly crystalliza- ble. These products are tyrosine and the acid amides of the fatty series C n H 2im NO a , from amidobutyric acid, C 4 H 7 (NH 2 )0 2 , to amid-oenanthic acid, C 7 H 13 (NH 2 )0 2 , inclusive. With these products are others which are also crystallizable, but contain less hydrogen ; lastly, more highly oxidized amides are formed in the same reaction, such as malamic, diamidocitric, aspartic, and glutamic acids. From these results, it may be inferred that albumen and its analogues contain the elements of urea, tyrosine, acid amides of the fatty series, and more oxidized amides analogous to as- 56 662 ELEMENTS OF MODERN CHEMISTRY. partic acid, all of these bodies being combined together, with elimination of water. The presence of a certain proportion of a dextriniform body in the products of the decomposition of albumen permits the supposition that the complex molecule of the latter body contains also an amide of cellulose or an amy- laceous body. Action of the Salts on Albumen. Many salts precipitate solutions of albumen. Acetate and subacetate of lead form dense precipitates of albuminate of lead. Cupric sulphate pro- duces a blue precipitate. Corrosive sublimate yields a white precipitate, even in very dilute solutions of albumen. The in- solubility of this precipitate explains the use of albumen as an antidote to corrosive sublimate. Solutions of albumen are not precipitated by solutions of sodium chloride or sodium sulphate, but when acetic acid is added to the mixture, a precipitate forms. Reciprocally, a solu- tion of albumen to which acetic acid has been added is pre- cipitated by solutions of sodium chloride and sodium sulphate (Panum). When incinerated, both soluble and insoluble albumen leave a residue of calcium phosphate from which it is almost impos- sible to free the albumen. FIBRIN. When recently-drawn blood is left to itself, it coagulates spontaneously in a few minutes, and soon separates into a yel- low liquid called the serum, and a red coagulum, which is the dot. The clot contains the red corpuscles, imprisoned in an insoluble albuminoid matter. This matter is fibrin, and it is now considered to be formed during the coagulation at the ex- pense of two soluble substances, both of which exist in solution in the liquid portion of blood, which is called plasma. One of these substances is called fibrinogen, the other is the fibrino- plastic matter or paraglobulin. These two bodies have been isolated : when they are mixed in presence of water and a certain proportion of sodium chloride, the whole dissolves at first and the liquid soon coagulates spontaneously ; the coagu- lum is fibrin (Hoppe-Seyler). However this may be, fibrin may be obtained in fibrous masses by beating fresh blood. The latter does not coagulate in this case, but the coagulable constituent attaches itself in MYOSIN. 663 red flakes to the rods with which the blood is agitated. By washing these flakes in running water, they are freed from the adhering red corpuscles, and obtained in white or grayish elas- tic masses of a fibrous appearance. This substance is entirely insoluble in pure water, but dissolves in slightly alkaline solu- tions, and even, by the aid of a gentle heat, in solutions of certain salts which have an alkaline reaction. It decomposes hydrogen dioxide into oxygen and water. When left to itself during the heat of summer, it putrefies very rapidly, and is converted into a blackish liquid, which contains albumen. Leucine, and butyric and valeric acids are formed at the same time. When treated with concentrated hydrochloric acid, fibrin dissolves, forming a blue solution. When still moist fibrin is introduced into water containing one or two thousandths of concentrated hydrochloric acid, it swells and becomes trans- parent, forming a jelly. After some time it dissolves in the liquid, although with difficulty, and the solution then contains a substance which appears to be identical with syntonin (see farther on). When fibrin, swollen by hydrochloric acid, is digested at about 40 with gastric juice, or with the ferment called pepsin, which may be obtained from that liquid, the fibrin entirely dis- solves and is converted into a soluble and dialyzable body called peptone. This body is formed during the digestion of albu- minoid matters. Under certain circumstances sodium chloride dissolves fibrin. When such a solution is dialyzed, the salt passes into the exte- rior liquid, and there remains in the dialyzer a limpid solution having all the characters of a solution of albumen from egg (A. Gautier). MYOSIN. Kuhne has designated by this name the albuminoid matter which exists in solution in the sheaths of the muscular fibres (sarcolemma), and which has the property of coagulating spon- taneously after death, thus producing cadaveric rigidity. Myosin is insoluble in water as well as in a saturated solu- tion of common salt, but it dissolves in a solution containing ten per cent, of salt. It may be extracted from the muscles by the following process : the flesh is chopped up, and decolor- ized by washing with water ; it is then triturated with pul- 664 ELEMENTS OF MODERN CHEMISTRY. verized common salt, and enough water is added to produce a 10 per cent, solution of salt. After digestion for a few hours in the cold, the liquid is filtered and brought into contact with rock salt ; as the latter dissolves, it precipitates the myosin in flakes. Recently-precipitated myosin dissolves in a ten per cent, solution of salt, but it loses this property by desiccation. Very dilute hydrochloric acid dissolves it, and soon transforms it into syntonin. SYNTONIN. This substance may be extracted from muscular tissue. The latter is hashed, washed with water, and suspended in a large quantity of water containing one-thousandth of hydrochloric acid. The particles of meat swell and dissolve abundantly in the liquid, which is then pressed through a cloth, filtered, ana exactly neutralized with sodium carbonate. The syntonin is precipitated in gelatinous, colorless flakes, which collect and dry upon the filter in elastic films. Syntonin dissolves in water slightly acidulated with hydro- chloric acid. It also dissolves in lime-water, and in a one per cent, solution of sodium carbonate. HEMOGLOBIN. This name is given to the crystalline matter which may be extracted from red blood-corpuscles, and which was first called Jiematocrystalline. Preparation. Clotted blood is broken up and triturated with its own volume of water until it is entirely reduced. It is then passed through a cloth, and the liquid is frozen, or agitated with small quantities of ether until the corpuscles are dissolved. The thawed liquid, or that which has been treated with etlrer, deposits a coagulum which imprisons all of the unbroken corpuscles. The liquid is filtered, rendered slightly acid by acetic acid, and alcohol is added as long as the pre- cipitate first formed continues to dissolve. When cooled to for several hours, the red liquid sets in a mass of crystals ; these are collected on a filter, pressed, and washed with dilute alcohol and water, both at 0. They are purified by dissolving them in water at 40 and evaporating the solution in a vacuum, or by adding alcohol and cooling the liquid to 0. HEMOGLOBIN. 665 Composition. Hemoglobin so prepared has about the same composition as albuminoid bodies, but contains a little iron. According to Hoppe-Seyler, its composition is Carbon 54.18 Hydrogen 7.2 Nitrogen 16.2 Oxygen 21.5 Iron 0.42 Sulphur 0.7 Properties. Hemoglobin forms crystals which differ accord- ing to the blood from which they have been obtained. They generally belong to the type of the right rhombic prism. Those from human blood pre- sent, under the microscope, the forms indicated in Fig. 132. They are red, and doubly re- fracting. They contain water of crystallization. They dissolve in water, and more readily in slightly alkaline solutions. The red solution of hemo- globin (oxyhemoglobin) has an important optical property. When light which has trav- ersed a dilute notation of hemo- globin is decomposed by a prism, the spectrum so formed shows two black bands (absorp- tion bands) between Fraunhofer's lines D and E (Stokes). The crystals of hemoglobin contain oxygen which is weakly combined, and which may be removed by exposing the crys- tals in a vacuum (Hoppe-Seyler). Oxygenated hemoglobin is known as oxyhemoglobin, and hemoglobin deprived of oxygen reabsorbs that gas when brought into contact with it. It is curious that carbon monoxide will expel the oxygen from hemo- globin, at the same time replacing it (Cl. Bernard). The com- bination of hemoglobin and carbon monoxide is soluble in water. The solution of oxyhemoglobin yields its oxygen to certain reducing agents, such as hydrogen sulphide. Reduced hemo- globin gives an absorption spectrum containing one single band, 66* FIG. 132. 666 ELEMENTS OP MODERN CHEMISTRY. situated in a position between the two absorption-bands of oxy- hemoglobin. Hemoglobin decomposes hydrogen dioxide. It is very un- stable, and if the crystals be dried at a temperature above 100 they rapidly become altered. The aqueous solution decom- poses spontaneously in a few hours at 15, or temperatures above that point. The acids, even the weak ones, favor this decomposition, which is manifested by a change of color, the fine red tint of the hemoglobin being replaced by a brown. In these cases, hemoglobin decomposes into an albuminoid matter (globulin), and a ferruginous pigment called hematin. At the same time, small quantities of fatty acids are set free (Hoppe- Seyler). Hematin. This substance has received different names. Lecauu, who first studied it, named it hematosin. When prop- erly purified, it forms a blackish-blue, amorphous powder, which is quite stable, since it resists a temperature of 180. It con- tains carbon, hydrogen, nitrogen, oxygen, and iron. When incinerated, it leaves 12.8 per cent, of oxide of iron. It is insoluble in water, alcohol, ether, and chloroform. It dissolves in the alkalies, in ammonia, and in the acids, and is readily soluble in ammoniacal alcohol and in alcohol containing hydrochloric acid. These solutions are reddish-brown. With hydrochloric acid, hematin forms a compound which crystallizes in rhomboidal laminae ; the crystals are characteristic and may be recognized by means of the microscope (hydrochloride of hematin). Hematoidin. This body is doubtless a product of the decomposition of hemoglobin. Virchow found it in orange- colored crystals in the remains of old hemorrhages of the brain. It is also found in blood which has been exposed to air, and in extravasated blood in the Graefian follicles. It may easily be obtained from the yellow bodies contained in the ovaries of the cow, by triturating them with glass, and digesting for a few days with chloroform. After evaporation of the yellow chloro- form solution, the residue is treated with ether to dissolve out the fat. Hematoidin crystallizes in small, orange-red, transparent prisms. It is insoluble in water and alcohol, slightly soluble in ether ; it is soluble in chloroform, which it colors golden- yellow. It presents certain analogies with bilirubin (page 673). GLOBULIN CASEIN GELATIN. 667 GLOBULIN. Berzelius gave this name to the coagulable albuminoid sub- stance which may be obtained from red blood-corpuscles, and which is now believed to be a product of the decomposition of hemoglobin. This, or an analogous substance, exists in the crystalline lens. It may be obtained by boiling the crystalline lens of the ox with water and filtering the liquid. A solution of globulin is thus obtained. It much resembles albumen in its properties. When heated, it becomes clouded at 73, but coagulates completely only at 93. It is not precipitated by either acetic acid or by the alkalies, but when its acid or alkaline solution is neutralized, a precipitate is formed. A solution of globulin is precipitated by a current of carbon di- oxide. CASEIN. When an acid is added to milk, a thick precipitate is at once formed ; it is produced by the casein. The lactic acid which forms in milk by the fermentation of the milk-sugar, produces the same precipitation. The milk is then said to curdle. The precipitate consists of an albuminoid matter called casein, which is considered to be identical with coagulated albumen. Casein dissolves in alkaline liquids and even in certain alka- line salts, such as carbonate and phosphate of sodium. It exists in this state in milk, which is alkaline when fresh. When this solution of alkaline albuminate, to which the name soluble casein has been given, is evaporated, it becomes covered with a pellicle. Acetic acid precipitates it in flakes, combining with the alkali. It is also coagulated by the gastric juice, which is acid, and which contains a ferment known as pepsin. This ferment exists in rennet which is prepared from the fourth stomach of the calf, and which serves to coagulate skimmed milk in the preparation of cheese. Indeed, casein, more or less altered by putrefaction, is the basis of the different kinds of cheese. GELATIN. The bones contain a cartilaginous substance, which may be isolated by dissolving out the mineral salts, which consist of calcium carbonate and phosphate, with hydrochloric acid. 668 ELEMENTS OP MODERN CHEMISTRY. There remains a semi-transparent, elastic substance, which re- tains the form of the bone. This substance, which has been called ossein, or collagene, is insoluble in cold water, but by prolonged boiling, or more rapidly by digestion with water heated to a few degrees above 100, it dissolves and forms a solution, which sets in a transparent jelly on cooling. The body formed by this transformation dissolves slightly in cold water, and abundantly in boiling water, and the hot solution forms a jelly on cooling. Hence the name gelatin. Other tissues of the animal economy may be converted into gelatin by boiling with water. It is so with the cellular tissue, the skin, the scales, and swimming-bladder of fishes. The swimming-bladder of the sturgeon, known in commerce as fish- glue, furnishes very pure gelatin by boiling with water. The substances which may*be converted into gelatin possess very nearly the same composition as gelatin itself; hence no- thing precise is known concerning the nature of the change produced in them by the action of boiling water. Dry gelatin occurs in transparent sheets, which are sonorous, and of which the color varies from yellowish to brown, accord- ing to their thickness and purity. The aqueous solution is precipitated in white flakes by alco- hol. The acids do not precipitate it, with the exception of tannic acid, with which it forms a thick coagulum, a combina- tion of tannin and gelatin. This action of tannin on gelatinous matters is applied in the manufacture of leather, which is ob- tained by leaving fresh or green skins, previously swelled by soaking in water, in contact with tan, that is, coarsely-ground oak-bark, which is well known to contain tannin. When chlorine-water is added to a solution of gelatin, a white cloud is formed which an excess of chlorine converts into a white, flocculent precipitate. Solutions of gelatin are precipitated by platinic chloride and by corrosive sublimate, but not by alum or the salts of lead, copper, silver, etc. When boiled with dilute sulphuric acid, gelatin is converted into leucine and a substance to which Braconnot gave the name sugar of gelatin, and which is gly- cocol. Chondrin. When the cartilages of the short ribs are boiled for a very long time with water, they dissolve, forming a liquid which sets in a jelly on cooling. This gelatinous matter is chondrin. It is distinguished from gelatin by the property of RESPIRATION. 669 its aqueous solution to form precipitates with all the acids, and with a great number of metallic salts. Alum forms in it an abundant, flocculent precipitate. The substances which have just been summarily described, and others which form the liquids an dtissues of the animal economy, undergo various transformations in the organism. They are derived from the vegetable kingdom, which alone can elaborate such complex matters. They pass with the aliments into the animal organisms, which assimilate them, and this work of assimilation does not profoundly modify the nitrogenized matters. But once fixed in the tissues, they do not remain there indefinitely, for there is a continual change and renewal of the whole economy. They become unfitted for the require- ments of life, and disappear in their turn, eliminated by that continual oxidation which makes of the body a permanent hearth of slow combustion. A notable portion of the oxygen which enters the lungs at each inhalation penetrates into the blood, and is converted in the capillary system and the intrica- cies of the tissues into carbon dioxide. This gas, which returns to the lungs with the venous blood, is exhaled at each exhala- tion. Expired air contains 4 to 5 per cent, of carbon dioxide. The carbon dioxide eliminates the greater portion of the carbon contained in the organic bodies burned during the phe- nomenon of respiration. The hydrogen of these bodies is eliminated in the form of water. But what becomes of their nitrogen ? In man, and a great number of the higher animals, it is eliminated in the urea contained in the urine. Such are the principal features of this grand function of respiration, the source of heat in all animals. But how is this slow oxidation which constitutes the object of respiration, as first shown by Lavoisier, accomplished ? Are the organic matters ready to be oxidized and consumed at once, or does the oxidation take place in successive phases, so that there are a certain number of intermediate terms between the complex products which must disappear and the final products of their oxidation ? All facts lead to the adoption of the latter conclusion. Indeed, there are found in the tissues and liquids of the economy a great number of bodies having compositions more or less complex, and which are the products, and, as it 670 ELEMENTS OF MODERN CHEMISTRY. were, the testimony of a successive simplification, of disas- Rimilation, as it is called. But it must not be supposed that all of the reactions which take place in the economy are phenomena of oxidation. Be- fore being definitely oxidized and rejected from the body, the ingested organic matters and those which form our humors and tissues, may undergo various transformations and sometimes molecular complications. In this respect, Dr. Ure's celebrated experiment is well known : having taken benzoic acid, he found hippuric acid in his urine. Analysis has shown the presence in the animal economy of a multitude of more or less complex organic compounds, nitrogenized and non-nitrogenized, having definite compositions, and which are the products of varied reactions. Such reactions take place in the blood and in the tissues, principally in glandular organs, such as the liver. As it would be impossible to consider all of these products of dis- assimilation, we can only briefly notice the more important. LECITHINE. Grobley has given this name to a phosphorized fatty matter, before noticed in the brain by Vauquelin. It exists in the brain and in the nerves. There is a closely allied body, recently described by Liebreich, under the name protagon. Grobley extracted lecithine from yolk of egg. That substance is exhausted with a mixture of alcohol and ether, and an alco- holic solution of cadmium chloride is added to the solution obtained ; a white, flocculent precipitate is formed, and is puri- fied by washing with alcohol and ether. This precipitate is a compound of cadmium chloride and hydrochloride of lecithine. It is suspended in ether and decomposed by hydrogen sulphide : cadmium sulphide is precipitated and hydrochloride of lecithine remains in solution, and may be obtained on evaporation in a wax-like mass. When the alcoholic solution of this hydro- chloride is decomposed by silver oxide, the lecithine is set free, and remains, after evaporation, in the form of a homogeneous, translucent mass. Lecithine may also be precipitated by pla- tinic chloride instead of cadmium chloride (Strecker). Lecithine and all of its compounds are very alterable. It decomposes rapidly when the alcoholic solution of its hydro- chloride is boiled with baryta-water ; oleate and palmitate of CHOLESTERIN. 671 barium are precipitated, phosphoglycerate of barium is formed, and an organic base called neuriiie remains in solution (Lieb- reich). Strecker represents this interesting decomposition by the equation 3H2Q = C 3 IFP0 6 + C5R15N0 2 Lecithine. Phospho- Neurine. Oleic Palmitic glyceric acid. acid. acid. Neurine is an oxygenized base of which the constitution is known. It is the hydrate of trimethyl-hydroxethylene-ammo- nium (page 527). (C2H>.OH)' ) The chloride of this ammoniated base is formed by synthesis by the action of ethylene chlorohydrate on trimethylamine (A. Wurtz). Trimetliyl-hydroxethylene- auimuniuiu chloride. Neurine is identical with a base which Strecker obtained from the bile and designated as cholme. CHOLESTERIN. This body is largely diffused in the organism. It exists in the bile, and is the principal constituent of most biliary cal- culi. It is found also in small quantity in the serum of blood, in the brain, in yolk of egg, pus, the liquid of hydrocele, etc. Its solubility in alcohol and especially in ether, and the facility with which it crystallizes from its solutions, permits its easy isolation. Cholesterin ordinarily deposits in thin and brilliant, rhombic plates. It melts at 145, and can be sub- limed, out of contact with air, at 360. It forms neutral compounds with acids, analogous to the ethers ; it seems to be a monatomic alcohol. The principal organic constituents of the bile are two com- plex acids, both nitrogenized, and one of which contains sul- phur. These are glycocholic and taurocholic acids. They are 672 ELEMENTS OF MODERN CHEMISTRY. not contained in the bile of all animals, and are generally ex- tracted from that of the ox. They enter into the composition of human bile, which contains in addition coloring matters of which the most important is bilirubin. We will briefly describe these bodies. GLYCOCHOLIC ACID. This body exists in the bile in the form of sodium glycocho- late, which salt may be obtained in crystals from ox's bile. The latter is decolorized by animal charcoal, filtered, the liquid evaporated, and the residue perfectly dried and dissolved in absolute alcohol ; the solution is introduced into a flask, and ether is cautiously added so that the two liquids may not mix, but form two layers. The latter gradually mingle and the sodium glycocholate deposits in crystals (Plattner). When dilute sulphuric acid is added to a solution of this salt, a cloud is formed, and glycocholic acid is soon deposited in fine needles. This acid is only slightly soluble in water and ether, but dis- solves in alcohol. It is dextrogyrate (Hoppe-Seyler). By the action of hydrochloric acid, it is decomposed into cholalic acid and glycocol (Strecker). C 26 H 43 N0 6 _|_ H 2 = C24 H 4<, 5 + C 2 H 5 N0 2 Glycocholic acid. Cholalic acid. Glycocol. Cholalic Acid exists in the amorphous state and crystallized. It deposits from its ethereal solution in four-sided prisms, beveled at the ends, and containing two molecules of water of crystallization. By boiling with acids, it is converted into a resinous body which Berzelius called dy sly sin. C 24 H 4o 5 ^ C 24 H 36 3 + 2H 2 Dyslysin. TAUROCHOLIC ACID. C 26 H* 5 NSO 7 The sodium salt of this acid remains dissolved in the ethe- real solution from which sodium glycocholate has deposited. It has not yet been obtained crystallized. It is dextrogyrate. When boiled with dilute acids, or with alkalies, it breaks up into cholalic acid and taurine (Strecker). BILIRUBIN BILIVERDIN. 673 C 26 H 45 NS0 7 + H 2 = C^H^O 5 + C 2 H T NS0 3 Taurocholic acid. Cholalic acid. Tauriiie. Taurine, which was discovered by Leopold Grmelin, has already been described (page 528). BILIRUBIN. C 16 H 18 N 2 3 This substance exists in human bile and in biliary calculi. It may be extracted from the latter, which contain it as calcu- lary pigment. They are crushed, and exhausted, first with ether, which removes the cholesterin, then with boiling water, and finally with chloroform. The coloring matter remains in the residue as a calcareous combination ; this is decomposed by adding hydrochloric acid, evaporating to dryness, and ex- hausting the dried residue with chloroform. After evaporation, the chloroform solution leaves a residue which contains, inde- pendently of bilirubin, three other biliary pigments which we will only mention : biliprasin, bilifuscin, and bilihumin. Alco- hol dissolves the bilifuscin from this residue, and the new residue is exhausted with chloroform, which takes up the bili- rubin, which alcohol precipitates in orange-colored flakes from the chloroform solution. Bilirubin is obtained in small, dark-red crystals by evapora- tion of its solution in chloroform. It is insoluble in water, and very slightly soluble in ether and alcohol, but dissolves in chlo- roform, benzol, and carbon disulphide. It is very soluble in the alkalies, forming an orange-red solution, which becomes pure yellow on addition of water, and from which hydrochloric acid precipitates bilirubin. The ammoniacal solution of bili- rubin gives precipitates with calcium chloride, barium chloride, and lead acetate. BILIVERDIN. When a solution of bilirubin in sodium hydrate is agitated with air, it absorbs oxygen and becomes green. Hydrochloric acid precipitates biliverdin from the solution. It is a bright green powder, insoluble in water, ether, and chloroform, but soluble in alcohol. It contains one more atom of oxygen than bilirubin. 2D 57 674 ELEMENTS OP MODERN CHEMISTRY. We may add that other coloring matters have also been derived from bile. They are bilifuscin, C 16 H 20 N 2 4 , biliprasin, C M H M N0 8 , and bilihumin. CREATINE. C*HN0 2 + H2Q This body was discovered by Chevreul in meat broth. It exists ready formed in the muscles, and passes into the extract of meat. It may be prepared by treating the solution of this extract with basic acetate of lead, filtering, freeing the filtrate from excess of lead by hydrogen sulphide, and evaporating the solution at a gentle heat until it crystallizes. The crystals are separated from the mother-liquor, and alcohol added to the latter precipitates a fresh quantity of creatine (Neubauer.) Creatine crystallizes in brilliant, colorless, oblique rhombic prisms, containing one molecule of water, which they lose at 100, becoming opaque. By the action of acids or by long boiling with water, crea- tine is converted into creatinine. C 4 H 9 N 3Q 2 = c 4 H 7 N 3 + H 2 Creatine. Creatinine. When creatine is boiled with baryta-water, it is converted into sarcosine, ammonia being disengaged and barium carbon- ate precipitated at the same time. It is generally considered that the ammonia and carbon dioxide are produced in this case at the expense of urea, which is formed directly by the decom- position of creatine. C 4 H 9 N 3 2 + H 2 = C 3 H 7 N0 2 + CH 4 N 2 Creatine. Sarcosine. Urea. Sarcosine is methylglycocol. It is isomeric with lactamide and alanine. It may be obtained artificially by treating mono- chloracetic acid with methylamine (Volhard.) C2H2C10.0H + CH3.NH2 = CH20<^ (CH8) + HC1 Monochloracetic acid. Methylamine. Sarcosine. Volhard has made the synthesis of creatine by the action of cyanamide on sarcosine. Cyanamide, CN.NH 2 , represents am- monium cyanate less the elements of water. CN 2 H 2 + C 3 H 7 N0 2 = C 4 !PN 3 2 Cyanamide. Sarcosine. Creatine. CREATININE. 675 CREATININE. OH'NH) This body exists in muscular tissue independently of creatine. It may be precipitated from the mother-liquor from which the latter body has deposited, by adding an alcoholic solution of zinc chloride, which forms a crystalline combination with the creatinine. Creatinine crystallizes in oblique rhombic prisms. It is much more soluble in alcohol than creatine. It has basic properties, and forms a crystallizable compound with hydrochloric acid. Creatine and creatinine have been found not only in the muscles, but in small quantities in the brain, blood, and urine. Among the products of disassimilation we may also mention : Leucine, C 6 H 13 N0 2 , which belongs to the homologous series of glycocol, and is found in many organs, especially in the pancreas, the salivary glands, the spleen, and the liver (page 546). Tyrosine, C 9 H n N0 3 , a body crystallizing in fine needles may be obtained from the pancreas and the spleen (page 631). It is known also that leucine and tyrosine may be obtained directly by the action of alkalies upon complex nitrogenized matters (page 661). Hippuric acid, C 9 H 9 N0 3 , the origin of which has already been indicated (page 62*7). Uric acid, C 5 H 4 N*0 3 , which exists in small quantity in human urine, and which constitutes a large proportion of the urine of birds and reptiles (page 559). Allantoin, C 4 H 6 N 4 3 , a product of the oxidation of uric acid, which Vauquelin and Buniva formerly extracted from the am- niotic liquor of the cow, and which has also been found in the urine of young calves (page 563). Various other products are related to uric acid. They are : Xanthine, C 5 H 4 N 4 2 , a yellow matter, which Proust discov- ered in certain rare calculi (xanthic calculi), and which has also been found in small quantity in the muscles, pancreas, liver, and urine. 57* 676 ELEMENTS OF MODERN CHEMISTRY. Hypoxanthine or sarcine, C 5 H 4 N 4 0, a white, amorphous sub- stance which Scherer obtained from the spleen, and of which Strecker has noticed the existence in muscular tissue. Hypo- xanthine forms a crystallizable combination with hydrochloric acid. It presents interesting relations of composition with xan- thine and uric acid. Uric acid , . . C 5 H*N*0 3 Xanthine CSHWO* Hypoxanthine C5H*N*0 When hypoxanthine is boiled with nitric acid, it is converted into a nitrogenized body. By the action of reducing agents, such as ferrous sulphate, this nitrogenized body is converted into guanine, C 5 H 5 N 3 0. The latter body was first obtained from guano. It has been found in the tissue of the pancreas. MEASURES OF WEIGHT. 1 Milligramme 1 Centigramme 1 Decigramme 1 Gramme 1 Decagramme 1 Hectogramme 1 Kilogramme GRAINS. 0.01543 0.15432 1.54323 15.43234 154.32349 1543.23488 15432.34880 OUNCES TROT = 480 GRAINS. 0.000032 0.000321 0.003215 0.032150 0.321507 3.215072 32.150726 POUNDS AVOIRDUPOIS. 0.0000022 0.0000220 0.0002204 0.0022046 0.0220462 0.2204621 2.2046212 1 Grain = 0.064799 grammes. 1 Oz. Troy = 31.103496 " 1 Lb. Avoirdupois = 0.453495 kilogrammes. 1 Cubic Centimetre of water weighs 1 gramme. To convert Centigrade degrees into Fahrenheit degrees, multiply by 9 and divide by 5 ; add 32. To convert Fahrenheit degrees into Centigrade degrees, subtract 32, then multiply by 5 and divide by 9. 1 Metre = 39.370708 inches. 1 Centimetre = 0.39370 " 1 Millimetre = 0.03937 " llnch = 2.539954 centimetres. 677 INDEX. Acetamide, 505. Acetates, 495. Acetic anhydride, 499. Acetone, 503. Acetones, 420. Acetonitrile, 449. Acetyl chloride, 502. Acetylene, 520. Acid, 42. acetic, 492. aconitic, 559. acrylic, 512. alloxanic, 561. amidacetic, 544. /3-amidopropionic, 546. anisic, 631. anthranilic, 634. antimonic, 189. arsenic, 182. arsenious, 179. aspartic, 554. benzole, 626. boric, 193. bromic, 130. butyric, 508. campholic, 601. camphoric, 602. caproic, 510. carbonic, 206, 209. cerotic, 511. chlorethylsulphurous, 528. chloric, 125. chlorous, 123. cholalic, 672. chromic, 347. cinchonic, 654. citraconic, 559. citric, 558. crotonic, 512. cyanic, 438. cyan uric, 442. dialuric, 562. dibromosuccinic, 551. digallic, 590. Acid, elaidic, 512. ethylnitrolic, 467. ethylphosphinic, 485. ethylsulphuric, 468. formic, 490. fumaric, 553. gallic, 632. gluconic, 570. glutamic, 659. glyceric, 543. glycocholic, 672. glycollic, 537. glyoxylic, 538. hippuric, 627. hydracrylic, 543. hydriodic, 132. hydrobromic, 128. hydrochloric, 116. hydrocyanic, 431. hydrofluoric, 136. hydrofluosilicic, 198. hydrosulphurous, 100. hypobromous, 129. hypochlorous, 122. hypophosphorous, 171. hyposulphuric, 109. hyposulphurous, 109. iodic, 134. iodopropionic, 508. isethionic, 528. isobutyric, 509. isophthalic, 638. itaconic, 559. lactic, 539. leucic, 546. maleic, 553. malic, 552. malonic, 536. manganic, 343. margaric, 511. meconic, 646. mellic, 593. mesoxalic, 561. metaphosphoric, 175. 679 680 ELEMENTS OF MODERN CHEMISTRY. Acid, methylnitrolic, 451. monobromosuccinic, 551. monochloracetic, 498. nitric, 157. nitrohydrochloric, 160. oleic, 512. opianic, 650. oxalic, 547. oxamic, 550. oxybenzoic, 631. palmitic, 511. parabanic, 562. paralactic, 539, 541. paratartaric, 558. paroxybenzoic, 631. pentathionic, 97. perbromic, 130. perchloric, 125. perchromic, 87. periodic, 135. permanganic, 344. persulphuric, 110. phosphoric, 173. phosphorous, 172. phthalic, 637. picramic, 607. picric, 607. propionic, 507. purpuric, 563. pyrogallic, 633. pyrophosphoric, 174. pyrotartaric, 555. pyruvic, 555. quinic, 651. quinolic, 653. ruberythric, 642. salicylic, 629. silicic, 199. stannic, 354. stearic, 511. succinic, 550. sulphocarbonic, 215. sulphosulphuric, 109. sulphuric, 102. " fuming, 108. sulphurous, 97. tannic, 589. tartaric, 554. tartronic, 556. taurocholic, 672. terephthalic, 638. tetrathionic, 97. trichloracetic, 499. trithionic, 97. uric, 559, 675. Acid, valeric, 510. Acids, diatomic, 428. fatty, 488, 505. monatomic, 418. polyatomic, 536. Aconitine, 655. Acrolein, 512. Affinity, 11. Air, 63. Alanine, 545. Albumen, 660. Albuminoid matters, 657. Alcohol radicals, 425. Alcohol, allyl, 478. ainyl, 475. benzyl, 623. butyl, 474. cetyl, 477. ethyl, 455. heptyl, 477. hexyl, 477. methyl, 447. octyl, 477. propyl, 474. Alcohols, diatomic, 427, 521. monatomic, 417, 444, 472. polyatomic, 429, 564. primary, secondary, tertiary, 472. Aldehyde, acetic, 505. anisic, 631. benzoic, 624. butyric, 509. crotonic, 512. formic, 492. salicylic, 628. Aldehydes, 420. Aldol, 501. Alizarin, 641. Alkaloids, 643. Allantoin, 563. Alloxan, 561. Alloxantin, 562. Alloys, 236. Allyl alcohol, 478. bromide, 518. iodide, 478. sulphide, 478. sulphocyanate, 478. Alum, 315. Aluminium, 313. chloride, 314. oxide, 314. silicates, 317. sulphate, 316 INDEX. 681 Amalgams, 236. Amides, 421. Amines, 422, 479. Ammonia, 139. action of Cl and I, 143. action of potassium, 145. Ammonium amalgam, 145. carbonate, 148. chloride, 146. cyanate, 440. formate, 491. nitrate, 148. oxalate, 549. sulphate, 149. sulphide, 147. sulphoeyanate, 444. sulphydrate, 147. theory of, 146. Amygdalin, 587. Auiyl alcohols, 475. chloride, 476. iodide. 476. oxide, 476. Ainyk-nes, 519. bromides, 520. Anilides, 609. Aniline, 608. colors, 613. salts, 608. Anisic compounds, 631. Anthracene, 640. Anthracite, 202. Anthraquinone, 641. Antimonio-potassiutn tartrate, 557. Antimony, 185. antimonate, 188. oxide, 188. pentachloride, 187. pentasulphide, 190. pentoxide, 189. trichloride, 186. trisulphide, 189. Apomorphine, 648. Aromatic compounds, 590. Arsenic, 176. chloride, 179. disulphide, 183. pentasulphide, 184. pontoxide, 182. trioxide, 179. trisulphide, 183. Arsines, 423. Asparagin, 553. Atomic heats, 34. Atomic theory, 27. 2D* Atomicity, theory of, 222. Atropine, 656. Aurin, 608. Australine, 598. Azobenzol, 604. Azoxybenzol, 604 Barium, 302. carbonate, 304. chloride, 303. dioxide, 302. nitrate, 303. oxide, 302. sulphate, 304. sulphide, 303. tests, 304. Beer, 579. Benzamide, 627. Benzol, 602. monobromo-, 603. monochloro-, 603. Benzoyl hydride, 624. chloride, 625. Benzyl alcohol, 623. aldehyde, 624. chloride, 620. Benzylamine, 624. Berthollet's laws, 265. Bilirubin, 673. Biliverdin, 673. Bismuth, 349. chloride, 350. nitrate, 351. oxide, 350. tests, 351. Bituminous coal, 202. Borneol, 602. Boron, 191. chloride, 192. fluoride, 193. oxide, 193. Boro-potassium tartrate, 558. Bromine, 127. Brucine, 654. Bunsen burner, 221. Butane, 455. Butyl alcohols, 474. Butylenes, 518. Butyral, 509. Butyrone, 509. Cacodyl, 453. Cadmium, 337. iodide, 337. oxide, 337. 682 ELEMENTS OF MODERN CHEMISTRY. Cadmium, sulphate, 338. sulphide, 337. Caesium, 300. Caffeine, 657. Calcium, 305. carbonate, 307. chloride, 307. hydrate, 305. hypochlorite, 309. lactate, 542. nitrate, 307. oxide, 305. sulphate, 308. tests, 310. Camphenes, 599. Camphor, 600. artificial, 591'. Carbamide, 440. Carbon, 200. dioxide, 209. disulphide, 215. estimation of, 406. monoxide, 207. compounds of, 438. oxysulphule, 216. tetrachoride, 449. sesquichloride, 516. Carbonates, 275. Carbonyl chloride, 208. Carbylamines, 450, 465. Casein, 667. Cellulose, 584. Charcoal, 202. absorbent properties of, 204. Chloral, 502. Chlorides, 246. monatomic, 415. of acid radicals, 421. Chlorine, 112. and Br and I, analogies, 136. peroxide, 124. Chloroform, 448. Chlorotoluols, 620. Chlorous anhydride, 123. Cholcsterin, 671. Chondrin, 668. Chromates, 347. Chromium, 346. chlorides, 348. oxides, 346. Cinchona bark, 650. Cinchonine, 653. Citrine, 600. Cobalt, 338. chloride, 339. Cobalt, oxides, 338. sulphate, 339. tests, 339. Cocaine, 655. Codeine, 648. Combination, laws of, 23-27. Combustion, 58. Conine, 644. Copper, 368. acetates, 496. alloys, 375. carbonates, 374. chlorides, 372. oxides, 371. sulphates, 373. sulphides, 372. tests, 375. Cotarnine, 650. Creatine, 674. Creatinine, 675. Cresols, 621. Cupellation, 359, 389. Cyanobenzol, 605. Cyanogen, 430. bromide, 437. chlorides, 436. iodide, 437. Cymene, 599. Dextrin, 581. Diamines, 428. Diamond, 201. Diazoamidobenzol, 612. Diazobenzol compounds, 610. Dichlorhydrin, 531. Dimethylarsinc, 453. Dioxindol, 636. Diphenylamine, 614. Diphenylketone, 627. Ductility, 233. Dulcite, 566. Elementary analysis, 406. Elements, table of, 39. Emulsin, 587. Epichlorhydrin, 531. Erythrite, 565. Ethane, 455. Ether, 459. acetylacetic, 498. Kay's, 449. Ethers compound, 41 9. simple, 454. Ethyl acetate, 497. carbamate, 470. INDEX. 683 Ethyl carbonate, 469. carbylamine, 465. chloride, 463. chlorocarbonate, 470. cyanate, 468. cyanide, 465. hydrate, 455. iodide, 464. nitrate, 467. nitrite, 466. oxalate, 549. oxide, 459. sulphate, 469. sulphide, 463. sulphydrate, 462. Ethylamines, 482. Ethylene, 513. acetates, 525. bromide, 515. chlorhydrate, 524. chloride, 515. chloro-derivatives, 515. diamines, 527. hydrate, 523. iodide, 515. nitrates, 525. oxide, 525. bases from, 526. Ethylhydrazine, 480. Ethylidene chloride, 501, 516. Ethylphosphines, 483. Fats, natural, 532. Fermentation, 576. Ferric chloride, 327. oxide, 326. sulphate, 329. Ferro-potassium tartrate, 557. Ferrous chloride, 327. lactate, 542. oxide, 325. sulphate, 328. Fibrin, 662. Flame, 218. Fluorescein, 638. Fluorine, 136. Formates, 491. Formonitrile, 432. Formulae, constitutional, empirical, rational, 419. Fulminates, 452. Functions, organic, 414. Gallium, 335. Gay-Lussac's law, 27. Gelatin, 667. Gilding, 394. Globulin, 667. Glucosan, 568. Glucose, 567. Glucosides, 586. Glycerin, 529. ethers of, 530. Glycocol, 544. Glycogen, 583. Glycol, 523. ethers of, 427. Glycol?, 427, 521. Glyoxal, 538. Gold, 391. * assay, 395. chlorides, 393. oxides, 393. Graphite, 201. Guanine, 676. Gum arable, 584. tragacanth, 584. Gums, 583. Gun-cotton, 586. Hematin, 666. Hemoglobin, 664. Hexamethylbenzol, 619. Homologous bodies, 405. Hydrazine, 480. Hydrazo benzol, 604. Hydrocarbons, C n H 2n + 2 , 415, 470. C n H* n , 517. OH 2n -2, 520. Hydrogen, 48. absorption by palladium, 51. antimonide, 186. arsenide, 178. dioxide, 85. estimation of, 406. persulphide, 96. phosphide, 165. silicide, 195. sulphide, 92. Hydroquinone, 616. Hydroxylamine, 149. Hypochlorous anhydride, 122. Hypoxanthine, 676. Indigo, 633. white, 634. Indium, 336. Indol, 636. Inosite, 571. Inulin, 583. 684 ELEMENTS OF MODERN CHEMISTRY. Iodine, 130. oxides, 134. Iron, 318. carbonate, 329. cast, 323. chlorides, 327. lactate, 542. oxides, 325. soft, 322. sulphates, 328. sulphides, 327. tests, 330. Isatin, 635. Isomerism, 412. Isomorphism, 37, 255. Isopropjl iodide, 474. Isoturpentine, 600. Kay's ether, 449. Lactamide, 542. Lactates, 542. Lactose, 574. Lamp-black, 203. Lead, 357. acetates, 496. carbonate, 366. chloride, 364. chromate, 367. dioxide, 362. iodide, 364. monoxide, 361. nitrate, 365. red oxide, 362. sulphate, 365. sulphide, 363. tests, 367. Lecithine, 670. Leucanilines, 612. Leucine, 546, 675. Levulosan, 570. Levulose, 570. Lignite, 202. Lime, 305. Lithium, 299. Magnesium, 310. carbonate, 312. citrate, 559. chloride, 311. oxide, 311. sulphate, 312. tests, 313. Malleability, 233. Maltose, 575. Manganese, 342. carbonate, 345. dioxide, 342. oxides, 342. sulphate, 344. tests, 345. Mannitan, 566. Mannite, 566. Marsh's apparatus, 181. Marsh gas, 445. Matches, 165. Mercur-ethyl, 486. Mercuric chloride, 380. iodide, 381. Mercur-methyl, 486. Mercurous chloride, 379. iodide, 381. Mercury, 375. cyanide, 433. fulminate, 452. nitrates, 382. oxides, 378. sulphates, 383. sulphide, 378. tests, 383. Mesitylene, 505. Metal dehyde, 501. Metallic carbonates, 275. chlorides, 246. hydrates, 244. nitrates, 271. oxides, 238. sulphates, 273. sulphides, 245. Metals, classification of, 277. general properties of, 231. Metamerism, 412. Methane, 445. Methylamines, 481. Methylbenzol, 618. Methyl bromide, 448. chloride, 448. compounds, 445. cyanide, 449. hydrate, 447. iodide, 448. nitrate, 450. nitrite, 450. oxide, 447. salicylate, 630. Mineral waters, 82. Minium, 362. Molecular weights, determination of, 410. Monobromobenzol, 603. INDEX. 685 Monochlorobenzol, 603. Monochlorhydrin, 531. Morphine, 647. Murexide, 563. Myosin, 663. Naphthalene, 639. Naphthol, 640. Naphthylamine, 640. Narceine, 646. Narcotine, 649. Neurine, 527, 671. Nickel, 340. chloride, 341. oxides, 340. sulphate, 341. tests, 341. Nicotine, 645. Nitrates, 271. Nitrethane, 466. Nitric anhydride, 157. Nitrobenzol, 604. Nitroferrocyanides, 436. Nitrogen, 138. chloride, 144. dioxide, 153. estimation of, 406. group, gen. considerations, 190. iodide, 145. monoxide, 151. pentoxide, 157. peroxide, 155. trioxide, 154. Nitroglycerin, 530. Nitromethane, 450. Nitrosyl chloride, 161. Nitrotoluols, 620. Nitryl, chloride and bromide, 156. Nomenclature, 37. Nornarcotine, 650. Notation, 37. Oils, essential, 596. fatty and drying, 533. Olein, 533. Opium, 646. Orcin, 486, 621. Organo-metallic compounds, 423. Orpiment, 183. Oxalates, 548. Oxamide, 549. Oxindol, 636. Oxygen, 54. Oxyphenols, 614. Ozone, 59. Palmitine, 533. Papaverine, 646. Paraconine, 645. Paraldehyde, 501. Persulphuric oxide, 110. Phenanthrene, 641. Phenol, 605. Phloretin, 589. Phloridzin, 588. Phloroglucin, 589, 618. Phosphines, 423. Phosphoric anhydride, 173. Phosphorus, 161. bromide, 169. iodide, 170. oxychloride, 169. pentachloride, 168. pentoxide, 173. sulphides, 176. sulphochloride, 159. trichloride, 168. Pinacolin, 505. Pinacone, 522. Platinum, 395. chlorides, 397. Plumbago, 201. Polymerism, 412. Populin, 588. Potassamide, 145. Potassium, 282. acetate, 495. acid-sulphate, 288. bromide, 286. carbonates, 289. chlorate, 288. chloride, 285. chromate, 347. cyanate, 439. cyanide, 433. dichromate, 347. ferricyanide, 435. ferrocyanide, 434. hydrate, 283. iodide, 285. methylate, 447. nitrate, 286. oxalates, 549. oxides, 283. perchl orate, 289. permanganate, 344. sulphate, 288. sulphides, 284. sulphocyanate, 444. tartrates, 556. tests, 290. 58 686 ELEMENTS OF MODERN CHEMISTRY. Pottery, 317. Propionitrile, 465. Propyl alcohols, 474. glycols, 529. iodide, 474. Propylene, 518. Prussian blue, 435. Pseudoinorphine, 647. Purpurin, 643. Pyrocatechin, 615. Pyrogallol, 618. Quinine, 651. Quinone, 616. Radicals, monatomic, 425. polyatomic, 426. Realgar, 183. Resorcin, 615. Respiration, 669. Richter's laws, 253. Rochelle salt, 556. Rosaniline, 611. Rubidium, 300. Saccharose, 571. Safety-lamp, 219. Salicin, 588. Salicyl hydride, 628. Saligenin, 588, 628. Salts, 43, 250. action of acids, 265. bases, 267. electricity, 262. heat, 261. metals, 264. salts, 268, 270. water, 256. neutral, acid, and basic, 252. Saponifieation, 535. Sarcine, 676. Sarcosine, 674. Selenium, 111. Silica, 199. Silicon, 194. chloride, 196. fluoride, 197. oxide, 199. Silver, 384. acetate, 497. assay, 389. chloride, 387. fulminate, 452. fulminating, 387. iodide, 388. Silver, nitrate, 388. oxide, 387. sulphide, 387. tests, 389. Silvering, 389. Soap, 534. Sodium, 291. acetate, 496. acid-carbonate, 298. acid-sulphate, 295. borate, 298. carbonate, 295. chloride, 293. hydrate, 292. hydrosulphite, 100. hyposulphite, 109. nitroferrocyanide, 436. oxides, 292. phosphates, 298. sulphate, 294. sulphide, 292. tests, 299. Sorbin, 571. Sorbite, 567. Specific heat, 34. Spectrum analysis, 300. Stannethyls, 487. Starch, 580. Stearin, 533. Stearin candles, 534. Steel, 323. Stibines, 423. Strontium, 304. Strychnine, 654. Succinic anhydride, 551. Succinyl chloride, 551. Sugar, cane, 571. grape, 567. inverted, 574. milk, 574. Sugars, 567. Sulphates, 273. Sulphur, 88. chlorides, 126. soft, 90. Sulphuric anhydride, 101. Sulphurous anhydride, 97. Sulphuryl chloride, 100, 106. Supersaturation, 259. Syntonin, 664. Tannin, 589. Tartar-emetic, 557. Tartrates, 556. Taurine, 528. INDEX. 687 Tellurium, 111. Terebene, 599. Terpileno, 600. Terpin, 598. Tetrachlorethylene, 516. Tetramethylammonium, 482. Tetrethylainmonium, 483. Thallium, 302. Thebaine, 646. Theine, 657. Theobromine, 656. Tin, 352. dichloride, 355. oxides, 354. sulphides, 355. tests, 357. tetrachloride, 356. Toluidines, 622. Toluol, 618. Tribenzylamine, 624. Trichlorhydrin, 532. Triethylamine, 483. Trimethylamine, 482. Trimethylcarbinol, 475. Trinitrophenol, 607. Turpentine, 596, 598. Tyrosine, 631. Urea, 440. Ureas, compound, 443. Urethane, 470. Verdigris, 497. Vermillion, 379. Vinegar, 494. Water, 70. analysis, 71. mineral, 82. natural state, 79. synthesis, 72. Wax, 477. Wine, 578. 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